diff --git a/docs/scip-ruby/CLI.md b/docs/scip-ruby/CLI.md
index 4d3132de5..b3d50a7fc 100644
--- a/docs/scip-ruby/CLI.md
+++ b/docs/scip-ruby/CLI.md
@@ -22,10 +22,14 @@ instead (`git rev-parse HEAD`).
 
 ## `--gem-map-path <arg>`
 
-At the moment, scip-ruby requires an extra step for cross-repo
-code navigation; you need to supply information about which
-file belongs to which gem explicitly, using a newline-delimited
-JSON file in the following format:
+For cross-repo navigation, scip-ruby needs to know which files
+belong to which gem. By default, scip-ruby will attempt to
+infer this from filepaths, assuming that files under `sorbet/rbi/{gems,annotations,dsl}/`
+belong to external gems as per the [standard layout](https://sorbet.org/docs/rbi#quickref).
+
+If you have files that contain definitions belonging to other gems,
+but are placed in non-standard directories, you can specify the correct gem information
+using a newline-delimited JSON file in the following format:
 
 <!-- 
 TODO: Uncomment this
@@ -46,16 +50,16 @@ newline-delimited JSON file in the following format:
 ...
 ```
 
-Then pass the path to the JSON file:
+Pass the path to the JSON file:
 
 ```bash
 scip-ruby --gem-map-path path/to/cross-repo-metadata.json
 ```
 
-Paths are interpreted relative to the working directory
+Paths in the JSON file are interpreted relative to the working directory
 for the `scip-ruby` invocation.
 
-If information about the gem being indexed
+If information about the primary gem being indexed (i.e. the one corresponding to the project root)
 cannot be inferred from the filesystem, then you can supply
 the `--gem-metadata` argument as described earlier.
 
@@ -69,11 +73,11 @@ and paths created by traversing directories.
 
 The path for emitting the SCIP index. Defaults to `index.scip`.
 
-## `--unquiet-errors`
+## `--unquiet`
 
 scip-ruby defaults to running in Sorbet's quiet mode, as scip-ruby supports
 indexing `# typed: false` files on a best-effort basis, but Sorbet may
 rightfully flag many errors in those files. The number of errors can be
 overwhelming if there is a large amount of untyped code.
 
-This flag restores Sorbet's default behavior.
\ No newline at end of file
+This flag restores Sorbet's default behavior.
diff --git a/scip_indexer/SCIPGemMetadata.cc b/scip_indexer/SCIPGemMetadata.cc
index 8a4983424..2e6d2a010 100644
--- a/scip_indexer/SCIPGemMetadata.cc
+++ b/scip_indexer/SCIPGemMetadata.cc
@@ -187,6 +187,31 @@ GemMapping::GemMapping()
     : currentGem(), map(), stdlibGem(make_shared<GemMetadata>(GemMetadata::tryParse("ruby@latest").value())),
       globalPlaceholderGem(make_shared<GemMetadata>(GemMetadata::tryParse("_global_@latest").value())) {}
 
+optional<shared_ptr<GemMetadata>> tryParseFilepath(std::string_view filepath) {
+    auto filenameStartIndex = filepath.find_last_of('/') + 1;
+    // E.g. foo/bar,
+    //      0123456 ; startIndex = 4, size = 7
+    auto filename = filepath.substr(filenameStartIndex, filepath.size() - filenameStartIndex);
+    auto dotIndex = filename.find_last_of('.');
+    if (dotIndex == std::string::npos) {
+        // Should have .rbi files here
+        return nullopt;
+    }
+    auto basename = filename.substr(0, dotIndex);
+    if (absl::StrContains(basename, '@')) {
+        auto metadata = GemMetadata::tryParse(basename);
+        ENFORCE(metadata.has_value());
+        return make_shared<GemMetadata>(metadata.value());
+    }
+    // TODO: Can we do better here by getting dependency versions from somewhere
+    // else, like Gemfile.lock? In practice, it looks like files under gems/ have associated
+    // versions, whereas files under annotations/ and gems/ do not have versions.
+    // Another potential option is to do two passes over the list of files; first collecting
+    // all external gem names+versions based on sorbet/rbi/gems, and then checking
+    // if the name here matches any known external gem name.
+    return make_shared<GemMetadata>(GemMetadata::forTest(string(basename), "latest"));
+}
+
 optional<shared_ptr<GemMetadata>> GemMapping::lookupGemForFile(const core::GlobalState &gs, core::FileRef file) const {
     ENFORCE(file.exists());
     auto it = this->map.find(file);
@@ -197,6 +222,19 @@ optional<shared_ptr<GemMetadata>> GemMapping::lookupGemForFile(const core::Globa
     if (absl::StartsWith(filepath, core::File::URL_PREFIX)) {
         return this->stdlibGem;
     }
+    // See https://sorbet.org/docs/rbi#quickref for description of the standard layout.
+    // Based on some Sourcegraph searches, it looks like RBI files can be named either
+    // gem_name.rbi or gem_name@version.rbi.
+    if (absl::StrContains(filepath, "sorbet/rbi/")) {
+        if (absl::StrContains(filepath, "sorbet/rbi/gems/") || absl::StrContains(filepath, "sorbet/rbi/annotations/") ||
+            absl::StrContains(filepath, "sorbet/rbi/dsl/")) {
+            auto metadata = tryParseFilepath(filepath);
+            if (metadata.has_value()) {
+                return metadata;
+            }
+        }
+        // hidden-definitions and todo.rbi get treated as part of the current gem
+    }
     if (this->currentGem.has_value()) {
         // TODO Should we enforce here in debug builds?
         // Fallback to this if set, to avoid collisions with other gems.
diff --git a/scip_indexer/SCIPGemMetadata.h b/scip_indexer/SCIPGemMetadata.h
index b9ef8bd06..86ba39066 100644
--- a/scip_indexer/SCIPGemMetadata.h
+++ b/scip_indexer/SCIPGemMetadata.h
@@ -4,6 +4,7 @@
 #include <memory>
 #include <optional>
 #include <string>
+#include <string_view>
 #include <utility>
 
 #include "absl/strings/str_split.h"
@@ -47,12 +48,12 @@ class GemMetadata final {
         return GemMetadata(name, version);
     }
 
-    static std::optional<GemMetadata> tryParse(const std::string &nameAndVersion) {
-        std::vector<std::string> v = absl::StrSplit(nameAndVersion, '@');
+    static std::optional<GemMetadata> tryParse(const std::string_view nameAndVersion) {
+        std::vector<std::string_view> v = absl::StrSplit(nameAndVersion, '@');
         if (v.size() != 2 || v[0].empty() || v[1].empty()) {
             return std::nullopt;
         }
-        return GemMetadata{v[0], v[1]};
+        return GemMetadata{std::string(v[0]), std::string(v[1])};
     }
 
     const std::string &name() const {
diff --git a/test/scip/testdata/multifile/infer-gem-map/current_gem.rb b/test/scip/testdata/multifile/infer-gem-map/current_gem.rb
new file mode 100644
index 000000000..3f1cba581
--- /dev/null
+++ b/test/scip/testdata/multifile/infer-gem-map/current_gem.rb
@@ -0,0 +1,7 @@
+# typed: true
+
+module CurrentGem
+  def gem_fun
+    puts 'Hello World'
+  end
+end
diff --git a/test/scip/testdata/multifile/infer-gem-map/current_gem.rbi b/test/scip/testdata/multifile/infer-gem-map/current_gem.rbi
new file mode 100644
index 000000000..42b3cfd82
--- /dev/null
+++ b/test/scip/testdata/multifile/infer-gem-map/current_gem.rbi
@@ -0,0 +1,5 @@
+# typed: true
+
+module CurrentGem
+  def gem_fun; end
+end
diff --git a/test/scip/testdata/multifile/infer-gem-map/current_gem.snapshot.rb b/test/scip/testdata/multifile/infer-gem-map/current_gem.snapshot.rb
new file mode 100644
index 000000000..465299164
--- /dev/null
+++ b/test/scip/testdata/multifile/infer-gem-map/current_gem.snapshot.rb
@@ -0,0 +1,9 @@
+ # typed: true
+ 
+ module CurrentGem
+#       ^^^^^^^^^^ definition currentgem 77 CurrentGem#
+   def gem_fun
+#      ^^^^^^^ definition currentgem 77 CurrentGem#gem_fun().
+     puts 'Hello World'
+   end
+ end
diff --git a/test/scip/testdata/multifile/infer-gem-map/current_gem.snapshot.rbi b/test/scip/testdata/multifile/infer-gem-map/current_gem.snapshot.rbi
new file mode 100644
index 000000000..59cca356c
--- /dev/null
+++ b/test/scip/testdata/multifile/infer-gem-map/current_gem.snapshot.rbi
@@ -0,0 +1,7 @@
+ # typed: true
+ 
+ module CurrentGem
+#       ^^^^^^^^^^ definition currentgem 77 CurrentGem#
+   def gem_fun; end
+#      ^^^^^^^ definition currentgem 77 CurrentGem#gem_fun().
+ end
diff --git a/test/scip/testdata/multifile/infer-gem-map/scip-ruby-args.rb b/test/scip/testdata/multifile/infer-gem-map/scip-ruby-args.rb
new file mode 100644
index 000000000..ade5ac525
--- /dev/null
+++ b/test/scip/testdata/multifile/infer-gem-map/scip-ruby-args.rb
@@ -0,0 +1 @@
+# gem-metadata: currentgem@77
diff --git a/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/annotations/annotgem.rbi b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/annotations/annotgem.rbi
new file mode 100644
index 000000000..27f911199
--- /dev/null
+++ b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/annotations/annotgem.rbi
@@ -0,0 +1,5 @@
+# typed: true
+
+module AnnotGem
+  def annot_fun; end
+end
diff --git a/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/annotations/annotgem.snapshot.rbi b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/annotations/annotgem.snapshot.rbi
new file mode 100644
index 000000000..d9a52306a
--- /dev/null
+++ b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/annotations/annotgem.snapshot.rbi
@@ -0,0 +1,7 @@
+ # typed: true
+ 
+ module AnnotGem
+#       ^^^^^^^^ definition annotgem latest AnnotGem#
+   def annot_fun; end
+#      ^^^^^^^^^ definition annotgem latest AnnotGem#annot_fun().
+ end
diff --git a/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/dsl/railsgem.rbi b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/dsl/railsgem.rbi
new file mode 100644
index 000000000..d271446b5
--- /dev/null
+++ b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/dsl/railsgem.rbi
@@ -0,0 +1,5 @@
+# typed: true
+
+module DSLGem
+  def create; end
+end
diff --git a/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/dsl/railsgem.snapshot.rbi b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/dsl/railsgem.snapshot.rbi
new file mode 100644
index 000000000..0e760635a
--- /dev/null
+++ b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/dsl/railsgem.snapshot.rbi
@@ -0,0 +1,7 @@
+ # typed: true
+ 
+ module DSLGem
+#       ^^^^^^ definition railsgem latest DSLGem#
+   def create; end
+#      ^^^^^^ definition railsgem latest DSLGem#create().
+ end
diff --git a/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/gems/extgem@99.rbi b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/gems/extgem@99.rbi
new file mode 100644
index 000000000..67b8988d3
--- /dev/null
+++ b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/gems/extgem@99.rbi
@@ -0,0 +1,5 @@
+# typed: true
+
+module ExternalGem
+  def ext_fun; end
+end
diff --git a/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/gems/extgem@99.snapshot.rbi b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/gems/extgem@99.snapshot.rbi
new file mode 100644
index 000000000..e91677376
--- /dev/null
+++ b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/gems/extgem@99.snapshot.rbi
@@ -0,0 +1,7 @@
+ # typed: true
+ 
+ module ExternalGem
+#       ^^^^^^^^^^^ definition extgem 99 ExternalGem#
+   def ext_fun; end
+#      ^^^^^^^ definition extgem 99 ExternalGem#ext_fun().
+ end
diff --git a/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/hidden-definitions/hidden.rbi b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/hidden-definitions/hidden.rbi
new file mode 100644
index 000000000..9afef5f28
--- /dev/null
+++ b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/hidden-definitions/hidden.rbi
@@ -0,0 +1,5 @@
+# typed: true
+
+module Hidden
+  def hidden_fun; end
+end
diff --git a/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/hidden-definitions/hidden.snapshot.rbi b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/hidden-definitions/hidden.snapshot.rbi
new file mode 100644
index 000000000..e88989fa7
--- /dev/null
+++ b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/hidden-definitions/hidden.snapshot.rbi
@@ -0,0 +1,7 @@
+ # typed: true
+ 
+ module Hidden
+#       ^^^^^^ definition currentgem 77 Hidden#
+   def hidden_fun; end
+#      ^^^^^^^^^^ definition currentgem 77 Hidden#hidden_fun().
+ end
diff --git a/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/todo.rbi b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/todo.rbi
new file mode 100644
index 000000000..b37011542
--- /dev/null
+++ b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/todo.rbi
@@ -0,0 +1,5 @@
+# typed: true
+
+module TODO
+  TODO_CONSTANT = 1
+end
diff --git a/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/todo.snapshot.rbi b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/todo.snapshot.rbi
new file mode 100644
index 000000000..0b9070ad3
--- /dev/null
+++ b/test/scip/testdata/multifile/infer-gem-map/sorbet/rbi/todo.snapshot.rbi
@@ -0,0 +1,8 @@
+ # typed: true
+ 
+ module TODO
+#       ^^^^ definition currentgem 77 TODO#
+   TODO_CONSTANT = 1
+#  ^^^^^^^^^^^^^ definition currentgem 77 TODO#TODO_CONSTANT.
+#  ^^^^^^^^^^^^^^^^^ reference currentgem 77 TODO#TODO_CONSTANT.
+ end
diff --git a/test/scip_test_runner.cc b/test/scip_test_runner.cc
index e118eda9a..baf9db49b 100644
--- a/test/scip_test_runner.cc
+++ b/test/scip_test_runner.cc
@@ -176,6 +176,51 @@ TEST_CASE("GemMapParsing") {
     ENFORCE(gemMap.lookupGemForFile(gs, unnormalized2).has_value());
 }
 
+// This test might feel a little redundant since we also have a similar integration test.
+// However, the integration test is making sure that the emitted index has the right
+// gem info, which is not checked by this test.
+TEST_CASE("GemInference") {
+    if (!onlyRunUnitTests) {
+        return;
+    }
+    vector<unique_ptr<core::Error>> errors;
+
+    auto logger = spdlog::stderr_color_mt("gem-inference-test");
+    auto errorCollector = make_shared<core::ErrorCollector>();
+    auto errorQueue = make_shared<core::ErrorQueue>(*logger, *logger, errorCollector);
+    core::GlobalState gs(errorQueue);
+    gs.initEmpty(); // needed for proper file table access
+
+    core::FileRef externalGemRBI, annotationsRBI, dslRBI, todoRBI, hiddenDefsRBI, notSorbetRBI;
+    {
+        core::UnfreezeFileTable fileTableAccess(gs);
+        externalGemRBI = gs.enterFile("./sorbet/rbi/gems/extgem@0.rbi", "");
+        annotationsRBI = gs.enterFile("./sorbet/rbi/annotations/myannot.rbi", "");
+        dslRBI = gs.enterFile("sorbet/rbi/dsl/myrails.rbi", "");
+        todoRBI = gs.enterFile("./sorbet/rbi/todo.rbi", "");
+        hiddenDefsRBI = gs.enterFile("./sorbet/rbi/hidden-definitions/hidden.rbi", "");
+        notSorbetRBI = gs.enterFile("myproject/x.rbi", "");
+    }
+
+    scip_indexer::GemMapping gemMap{};
+    gemMap.markCurrentGem(scip_indexer::GemMetadata::forTest("mygem", "33"));
+
+    auto checkGem = [&](core::FileRef file, string name, string version) {
+        auto gem = gemMap.lookupGemForFile(gs, file);
+        ENFORCE(gem.has_value());
+        ENFORCE(*gem->get() == scip_indexer::GemMetadata::forTest(name, version),
+                "\nexpected: name {}, version {}\nobtained: name {}, version {}", name, version, gem->get()->name(),
+                gem->get()->version());
+    };
+
+    checkGem(externalGemRBI, "extgem", "0");
+    checkGem(annotationsRBI, "myannot", "latest");
+    checkGem(dslRBI, "myrails", "latest");
+    checkGem(todoRBI, "mygem", "33");
+    checkGem(hiddenDefsRBI, "mygem", "33");
+    checkGem(notSorbetRBI, "mygem", "33");
+}
+
 // Copied from pipeline_test_runner.cc
 class CFGCollectorAndTyper { // TODO(varun): Copy this over to scip_test_runner.cc
 public: