diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 186422e5a90c0..6233b59dd7a47 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -18585,39 +18585,60 @@ namespace ts {
                         originalErrorInfo = undefined;
                     }
                 }
-                else if (isGenericMappedType(target) && !target.declaration.nameType) {
-                    // A source type T is related to a target type { [P in X]: T[P] }
-                    const template = getTemplateTypeFromMappedType(target);
+                else if (isGenericMappedType(target)) {
+                    // Check if source type `S` is related to target type `{ [P in Q]: T }` or `{ [P in Q as R]: T}`.
+                    const keysRemapped = !!target.declaration.nameType;
+                    const templateType = getTemplateTypeFromMappedType(target);
                     const modifiers = getMappedTypeModifiers(target);
                     if (!(modifiers & MappedTypeModifiers.ExcludeOptional)) {
-                        if (template.flags & TypeFlags.IndexedAccess && (template as IndexedAccessType).objectType === source &&
-                            (template as IndexedAccessType).indexType === getTypeParameterFromMappedType(target)) {
+                        // If the mapped type has shape `{ [P in Q]: T[P] }`,
+                        // source `S` is related to target if `T` = `S`, i.e. `S` is related to `{ [P in Q]: S[P] }`.
+                        if (!keysRemapped && templateType.flags & TypeFlags.IndexedAccess && (templateType as IndexedAccessType).objectType === source &&
+                            (templateType as IndexedAccessType).indexType === getTypeParameterFromMappedType(target)) {
                             return Ternary.True;
                         }
                         if (!isGenericMappedType(source)) {
-                            const targetConstraint = getConstraintTypeFromMappedType(target);
+                            // If target has shape `{ [P in Q as R]: T}`, then its keys have type `R`.
+                            // If target has shape `{ [P in Q]: T }`, then its keys have type `Q`.
+                            const targetKeys = keysRemapped ? getNameTypeFromMappedType(target)! : getConstraintTypeFromMappedType(target);
+                            // Type of the keys of source type `S`, i.e. `keyof S`.
                             const sourceKeys = getIndexType(source, /*stringsOnly*/ undefined, /*noIndexSignatures*/ true);
                             const includeOptional = modifiers & MappedTypeModifiers.IncludeOptional;
-                            const filteredByApplicability = includeOptional ? intersectTypes(targetConstraint, sourceKeys) : undefined;
-                            // A source type T is related to a target type { [P in Q]: X } if Q is related to keyof T and T[Q] is related to X.
-                            // A source type T is related to a target type { [P in Q]?: X } if some constituent Q' of Q is related to keyof T and T[Q'] is related to X.
+                            const filteredByApplicability = includeOptional ? intersectTypes(targetKeys, sourceKeys) : undefined;
+                            // A source type `S` is related to a target type `{ [P in Q]: T }` if `Q` is related to `keyof S` and `S[Q]` is related to `T`.
+                            // A source type `S` is related to a target type `{ [P in Q as R]: T }` if `R` is related to `keyof S` and `S[R]` is related to `T.
+                            // A source type `S` is related to a target type `{ [P in Q]?: T }` if some constituent `Q'` of `Q` is related to `keyof S` and `S[Q']` is related to `T`.
+                            // A source type `S` is related to a target type `{ [P in Q as R]?: T }` if some constituent `R'` of `R` is related to `keyof S` and `S[R']` is related to `T`.
                             if (includeOptional
                                 ? !(filteredByApplicability!.flags & TypeFlags.Never)
-                                : isRelatedTo(targetConstraint, sourceKeys)) {
-                                const templateType = getTemplateTypeFromMappedType(target);
+                                : isRelatedTo(targetKeys, sourceKeys)) {
                                 const typeParameter = getTypeParameterFromMappedType(target);
 
-                                // Fastpath: When the template has the form Obj[P] where P is the mapped type parameter, directly compare `source` with `Obj`
-                                // to avoid creating the (potentially very large) number of new intermediate types made by manufacturing `source[P]`
+                                // Fastpath: When the template type has the form `Obj[P]` where `P` is the mapped type parameter, directly compare source `S` with `Obj`
+                                // to avoid creating the (potentially very large) number of new intermediate types made by manufacturing `S[P]`.
                                 const nonNullComponent = extractTypesOfKind(templateType, ~TypeFlags.Nullable);
-                                if (nonNullComponent.flags & TypeFlags.IndexedAccess && (nonNullComponent as IndexedAccessType).indexType === typeParameter) {
+                                if (!keysRemapped && nonNullComponent.flags & TypeFlags.IndexedAccess && (nonNullComponent as IndexedAccessType).indexType === typeParameter) {
                                     if (result = isRelatedTo(source, (nonNullComponent as IndexedAccessType).objectType, reportErrors)) {
                                         return result;
                                     }
                                 }
                                 else {
-                                    const indexingType = filteredByApplicability ? getIntersectionType([filteredByApplicability, typeParameter]) : typeParameter;
+                                    // We need to compare the type of a property on the source type `S` to the type of the same property on the target type,
+                                    // so we need to construct an indexing type representing a property, and then use indexing type to index the source type for comparison.
+
+                                    // If the target type has shape `{ [P in Q]: T }`, then a property of the target has type `P`.
+                                    // If the target type has shape `{ [P in Q]?: T }`, then a property of the target has type `P`,
+                                    // but the property is optional, so we only want to compare properties `P` that are common between `keyof S` and `Q`.
+                                    // If the target type has shape `{ [P in Q as R]: T }`, then a property of the target has type `R`.
+                                    // If the target type has shape `{ [P in Q as R]?: T }`, then a property of the target has type `R`,
+                                    // but the property is optional, so we only want to compare properties `R` that are common between `keyof S` and `R`.
+                                    const indexingType = keysRemapped
+                                        ? (filteredByApplicability || targetKeys)
+                                        : filteredByApplicability
+                                            ? getIntersectionType([filteredByApplicability, typeParameter])
+                                            : typeParameter;
                                     const indexedAccessType = getIndexedAccessType(source, indexingType);
+                                    // Compare `S[indexingType]` to `T`, where `T` is the type of a property of the target type.
                                     if (result = isRelatedTo(indexedAccessType, templateType, reportErrors)) {
                                         return result;
                                     }
diff --git a/tests/baselines/reference/mappedTypeAsClauseRelationships.errors.txt b/tests/baselines/reference/mappedTypeAsClauseRelationships.errors.txt
new file mode 100644
index 0000000000000..98b164a866a27
--- /dev/null
+++ b/tests/baselines/reference/mappedTypeAsClauseRelationships.errors.txt
@@ -0,0 +1,40 @@
+tests/cases/conformance/types/mapped/mappedTypeAsClauseRelationships.ts(12,9): error TS2322: Type 'T' is not assignable to type 'Modify<T>'.
+tests/cases/conformance/types/mapped/mappedTypeAsClauseRelationships.ts(23,9): error TS2322: Type 'T' is not assignable to type 'FilterExclOpt<T>'.
+tests/cases/conformance/types/mapped/mappedTypeAsClauseRelationships.ts(24,9): error TS2322: Type 'T' is not assignable to type 'ModifyExclOpt<T>'.
+
+
+==== tests/cases/conformance/types/mapped/mappedTypeAsClauseRelationships.ts (3 errors) ====
+    // From original issue #45212:
+    type Methods<T> = { [P in keyof T as T[P] extends Function ? P : never]: T[P] };
+    type H<T> = T[keyof Methods<T>]; // Ok
+    
+    // `Filter<T>` only filters out some keys of `T`.
+    type Filter<T> = { [P in keyof T as T[P] extends Function ? P : never]: T[P] };
+    // `Modify<T>` might modify some keys of `T`.
+    type Modify<T> = { [P in keyof T as P extends string? `bool${P}`: P]: T[P] };
+    
+    function fun<T>(val: T) {
+        let x: Filter<T> = val; // Ok
+        let y: Modify<T> = val; // Error
+            ~
+!!! error TS2322: Type 'T' is not assignable to type 'Modify<T>'.
+    }
+    
+    type FilterInclOpt<T> = { [P in keyof T as T[P] extends Function ? P : never]+?: T[P] };
+    type ModifyInclOpt<T> = { [P in keyof T as P extends string? `bool${P}`: never ]+?: T[P] };
+    type FilterExclOpt<T> = { [P in keyof T as T[P] extends Function ? P : never]-?: T[P] };
+    type ModifyExclOpt<T> = { [P in keyof T as P extends string? `bool${P}`: never ]-?: T[P] };
+    
+    function fun2<T>(val: T) {
+        let x: FilterInclOpt<T> = val; // Ok
+        let y: ModifyInclOpt<T> = val; // Ok
+        let z: FilterExclOpt<T> = val; // Error
+            ~
+!!! error TS2322: Type 'T' is not assignable to type 'FilterExclOpt<T>'.
+        let w: ModifyExclOpt<T> = val; // Error
+            ~
+!!! error TS2322: Type 'T' is not assignable to type 'ModifyExclOpt<T>'.
+    }
+    
+    
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/mappedTypeAsClauseRelationships.js b/tests/baselines/reference/mappedTypeAsClauseRelationships.js
new file mode 100644
index 0000000000000..a1b0f68f9c2b5
--- /dev/null
+++ b/tests/baselines/reference/mappedTypeAsClauseRelationships.js
@@ -0,0 +1,41 @@
+//// [mappedTypeAsClauseRelationships.ts]
+// From original issue #45212:
+type Methods<T> = { [P in keyof T as T[P] extends Function ? P : never]: T[P] };
+type H<T> = T[keyof Methods<T>]; // Ok
+
+// `Filter<T>` only filters out some keys of `T`.
+type Filter<T> = { [P in keyof T as T[P] extends Function ? P : never]: T[P] };
+// `Modify<T>` might modify some keys of `T`.
+type Modify<T> = { [P in keyof T as P extends string? `bool${P}`: P]: T[P] };
+
+function fun<T>(val: T) {
+    let x: Filter<T> = val; // Ok
+    let y: Modify<T> = val; // Error
+}
+
+type FilterInclOpt<T> = { [P in keyof T as T[P] extends Function ? P : never]+?: T[P] };
+type ModifyInclOpt<T> = { [P in keyof T as P extends string? `bool${P}`: never ]+?: T[P] };
+type FilterExclOpt<T> = { [P in keyof T as T[P] extends Function ? P : never]-?: T[P] };
+type ModifyExclOpt<T> = { [P in keyof T as P extends string? `bool${P}`: never ]-?: T[P] };
+
+function fun2<T>(val: T) {
+    let x: FilterInclOpt<T> = val; // Ok
+    let y: ModifyInclOpt<T> = val; // Ok
+    let z: FilterExclOpt<T> = val; // Error
+    let w: ModifyExclOpt<T> = val; // Error
+}
+
+
+
+
+//// [mappedTypeAsClauseRelationships.js]
+function fun(val) {
+    var x = val; // Ok
+    var y = val; // Error
+}
+function fun2(val) {
+    var x = val; // Ok
+    var y = val; // Ok
+    var z = val; // Error
+    var w = val; // Error
+}
diff --git a/tests/baselines/reference/mappedTypeAsClauseRelationships.symbols b/tests/baselines/reference/mappedTypeAsClauseRelationships.symbols
new file mode 100644
index 0000000000000..629115cbd07f6
--- /dev/null
+++ b/tests/baselines/reference/mappedTypeAsClauseRelationships.symbols
@@ -0,0 +1,142 @@
+=== tests/cases/conformance/types/mapped/mappedTypeAsClauseRelationships.ts ===
+// From original issue #45212:
+type Methods<T> = { [P in keyof T as T[P] extends Function ? P : never]: T[P] };
+>Methods : Symbol(Methods, Decl(mappedTypeAsClauseRelationships.ts, 0, 0))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 1, 13))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 1, 21))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 1, 13))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 1, 13))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 1, 21))
+>Function : Symbol(Function, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 1, 21))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 1, 13))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 1, 21))
+
+type H<T> = T[keyof Methods<T>]; // Ok
+>H : Symbol(H, Decl(mappedTypeAsClauseRelationships.ts, 1, 80))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 2, 7))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 2, 7))
+>Methods : Symbol(Methods, Decl(mappedTypeAsClauseRelationships.ts, 0, 0))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 2, 7))
+
+// `Filter<T>` only filters out some keys of `T`.
+type Filter<T> = { [P in keyof T as T[P] extends Function ? P : never]: T[P] };
+>Filter : Symbol(Filter, Decl(mappedTypeAsClauseRelationships.ts, 2, 32))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 5, 12))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 5, 20))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 5, 12))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 5, 12))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 5, 20))
+>Function : Symbol(Function, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 5, 20))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 5, 12))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 5, 20))
+
+// `Modify<T>` might modify some keys of `T`.
+type Modify<T> = { [P in keyof T as P extends string? `bool${P}`: P]: T[P] };
+>Modify : Symbol(Modify, Decl(mappedTypeAsClauseRelationships.ts, 5, 79))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 7, 12))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 7, 20))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 7, 12))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 7, 20))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 7, 20))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 7, 20))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 7, 12))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 7, 20))
+
+function fun<T>(val: T) {
+>fun : Symbol(fun, Decl(mappedTypeAsClauseRelationships.ts, 7, 77))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 9, 13))
+>val : Symbol(val, Decl(mappedTypeAsClauseRelationships.ts, 9, 16))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 9, 13))
+
+    let x: Filter<T> = val; // Ok
+>x : Symbol(x, Decl(mappedTypeAsClauseRelationships.ts, 10, 7))
+>Filter : Symbol(Filter, Decl(mappedTypeAsClauseRelationships.ts, 2, 32))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 9, 13))
+>val : Symbol(val, Decl(mappedTypeAsClauseRelationships.ts, 9, 16))
+
+    let y: Modify<T> = val; // Error
+>y : Symbol(y, Decl(mappedTypeAsClauseRelationships.ts, 11, 7))
+>Modify : Symbol(Modify, Decl(mappedTypeAsClauseRelationships.ts, 5, 79))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 9, 13))
+>val : Symbol(val, Decl(mappedTypeAsClauseRelationships.ts, 9, 16))
+}
+
+type FilterInclOpt<T> = { [P in keyof T as T[P] extends Function ? P : never]+?: T[P] };
+>FilterInclOpt : Symbol(FilterInclOpt, Decl(mappedTypeAsClauseRelationships.ts, 12, 1))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 14, 19))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 14, 27))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 14, 19))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 14, 19))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 14, 27))
+>Function : Symbol(Function, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 14, 27))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 14, 19))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 14, 27))
+
+type ModifyInclOpt<T> = { [P in keyof T as P extends string? `bool${P}`: never ]+?: T[P] };
+>ModifyInclOpt : Symbol(ModifyInclOpt, Decl(mappedTypeAsClauseRelationships.ts, 14, 88))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 15, 19))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 15, 27))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 15, 19))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 15, 27))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 15, 27))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 15, 19))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 15, 27))
+
+type FilterExclOpt<T> = { [P in keyof T as T[P] extends Function ? P : never]-?: T[P] };
+>FilterExclOpt : Symbol(FilterExclOpt, Decl(mappedTypeAsClauseRelationships.ts, 15, 91))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 16, 19))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 16, 27))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 16, 19))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 16, 19))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 16, 27))
+>Function : Symbol(Function, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 16, 27))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 16, 19))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 16, 27))
+
+type ModifyExclOpt<T> = { [P in keyof T as P extends string? `bool${P}`: never ]-?: T[P] };
+>ModifyExclOpt : Symbol(ModifyExclOpt, Decl(mappedTypeAsClauseRelationships.ts, 16, 88))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 17, 19))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 17, 27))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 17, 19))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 17, 27))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 17, 27))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 17, 19))
+>P : Symbol(P, Decl(mappedTypeAsClauseRelationships.ts, 17, 27))
+
+function fun2<T>(val: T) {
+>fun2 : Symbol(fun2, Decl(mappedTypeAsClauseRelationships.ts, 17, 91))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 19, 14))
+>val : Symbol(val, Decl(mappedTypeAsClauseRelationships.ts, 19, 17))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 19, 14))
+
+    let x: FilterInclOpt<T> = val; // Ok
+>x : Symbol(x, Decl(mappedTypeAsClauseRelationships.ts, 20, 7))
+>FilterInclOpt : Symbol(FilterInclOpt, Decl(mappedTypeAsClauseRelationships.ts, 12, 1))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 19, 14))
+>val : Symbol(val, Decl(mappedTypeAsClauseRelationships.ts, 19, 17))
+
+    let y: ModifyInclOpt<T> = val; // Ok
+>y : Symbol(y, Decl(mappedTypeAsClauseRelationships.ts, 21, 7))
+>ModifyInclOpt : Symbol(ModifyInclOpt, Decl(mappedTypeAsClauseRelationships.ts, 14, 88))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 19, 14))
+>val : Symbol(val, Decl(mappedTypeAsClauseRelationships.ts, 19, 17))
+
+    let z: FilterExclOpt<T> = val; // Error
+>z : Symbol(z, Decl(mappedTypeAsClauseRelationships.ts, 22, 7))
+>FilterExclOpt : Symbol(FilterExclOpt, Decl(mappedTypeAsClauseRelationships.ts, 15, 91))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 19, 14))
+>val : Symbol(val, Decl(mappedTypeAsClauseRelationships.ts, 19, 17))
+
+    let w: ModifyExclOpt<T> = val; // Error
+>w : Symbol(w, Decl(mappedTypeAsClauseRelationships.ts, 23, 7))
+>ModifyExclOpt : Symbol(ModifyExclOpt, Decl(mappedTypeAsClauseRelationships.ts, 16, 88))
+>T : Symbol(T, Decl(mappedTypeAsClauseRelationships.ts, 19, 14))
+>val : Symbol(val, Decl(mappedTypeAsClauseRelationships.ts, 19, 17))
+}
+
+
+
diff --git a/tests/baselines/reference/mappedTypeAsClauseRelationships.types b/tests/baselines/reference/mappedTypeAsClauseRelationships.types
new file mode 100644
index 0000000000000..4136aab7cff07
--- /dev/null
+++ b/tests/baselines/reference/mappedTypeAsClauseRelationships.types
@@ -0,0 +1,64 @@
+=== tests/cases/conformance/types/mapped/mappedTypeAsClauseRelationships.ts ===
+// From original issue #45212:
+type Methods<T> = { [P in keyof T as T[P] extends Function ? P : never]: T[P] };
+>Methods : Methods<T>
+
+type H<T> = T[keyof Methods<T>]; // Ok
+>H : H<T>
+
+// `Filter<T>` only filters out some keys of `T`.
+type Filter<T> = { [P in keyof T as T[P] extends Function ? P : never]: T[P] };
+>Filter : Filter<T>
+
+// `Modify<T>` might modify some keys of `T`.
+type Modify<T> = { [P in keyof T as P extends string? `bool${P}`: P]: T[P] };
+>Modify : Modify<T>
+
+function fun<T>(val: T) {
+>fun : <T>(val: T) => void
+>val : T
+
+    let x: Filter<T> = val; // Ok
+>x : Filter<T>
+>val : T
+
+    let y: Modify<T> = val; // Error
+>y : Modify<T>
+>val : T
+}
+
+type FilterInclOpt<T> = { [P in keyof T as T[P] extends Function ? P : never]+?: T[P] };
+>FilterInclOpt : FilterInclOpt<T>
+
+type ModifyInclOpt<T> = { [P in keyof T as P extends string? `bool${P}`: never ]+?: T[P] };
+>ModifyInclOpt : ModifyInclOpt<T>
+
+type FilterExclOpt<T> = { [P in keyof T as T[P] extends Function ? P : never]-?: T[P] };
+>FilterExclOpt : FilterExclOpt<T>
+
+type ModifyExclOpt<T> = { [P in keyof T as P extends string? `bool${P}`: never ]-?: T[P] };
+>ModifyExclOpt : ModifyExclOpt<T>
+
+function fun2<T>(val: T) {
+>fun2 : <T>(val: T) => void
+>val : T
+
+    let x: FilterInclOpt<T> = val; // Ok
+>x : FilterInclOpt<T>
+>val : T
+
+    let y: ModifyInclOpt<T> = val; // Ok
+>y : ModifyInclOpt<T>
+>val : T
+
+    let z: FilterExclOpt<T> = val; // Error
+>z : FilterExclOpt<T>
+>val : T
+
+    let w: ModifyExclOpt<T> = val; // Error
+>w : ModifyExclOpt<T>
+>val : T
+}
+
+
+
diff --git a/tests/cases/conformance/types/mapped/mappedTypeAsClauseRelationships.ts b/tests/cases/conformance/types/mapped/mappedTypeAsClauseRelationships.ts
new file mode 100644
index 0000000000000..051192159e131
--- /dev/null
+++ b/tests/cases/conformance/types/mapped/mappedTypeAsClauseRelationships.ts
@@ -0,0 +1,27 @@
+// From original issue #45212:
+type Methods<T> = { [P in keyof T as T[P] extends Function ? P : never]: T[P] };
+type H<T> = T[keyof Methods<T>]; // Ok
+
+// `Filter<T>` only filters out some keys of `T`.
+type Filter<T> = { [P in keyof T as T[P] extends Function ? P : never]: T[P] };
+// `Modify<T>` might modify some keys of `T`.
+type Modify<T> = { [P in keyof T as P extends string? `bool${P}`: P]: T[P] };
+
+function fun<T>(val: T) {
+    let x: Filter<T> = val; // Ok
+    let y: Modify<T> = val; // Error
+}
+
+type FilterInclOpt<T> = { [P in keyof T as T[P] extends Function ? P : never]+?: T[P] };
+type ModifyInclOpt<T> = { [P in keyof T as P extends string? `bool${P}`: never ]+?: T[P] };
+type FilterExclOpt<T> = { [P in keyof T as T[P] extends Function ? P : never]-?: T[P] };
+type ModifyExclOpt<T> = { [P in keyof T as P extends string? `bool${P}`: never ]-?: T[P] };
+
+function fun2<T>(val: T) {
+    let x: FilterInclOpt<T> = val; // Ok
+    let y: ModifyInclOpt<T> = val; // Ok
+    let z: FilterExclOpt<T> = val; // Error
+    let w: ModifyExclOpt<T> = val; // Error
+}
+
+