diff --git a/CMakeLists.txt b/CMakeLists.txt
index b99fcfa8f..2afb0787e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -104,6 +104,14 @@ foreach(version ${_SwiftFoundation_versions})
     endforeach()
 endforeach()
 
+# wasi-libc emulation feature flags
+set(_SwiftFoundation_wasi_libc_flags)
+if(CMAKE_SYSTEM_NAME STREQUAL "WASI")
+    list(APPEND _SwiftFoundation_wasi_libc_flags
+        "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xcc -D_WASI_EMULATED_SIGNAL>"
+        "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xcc -D_WASI_EMULATED_MMAN>")
+endif()
+
 include(GNUInstallDirs)
 include(SwiftFoundationSwiftSupport)
 
diff --git a/Package.swift b/Package.swift
index 8a9807452..b2ab248eb 100644
--- a/Package.swift
+++ b/Package.swift
@@ -70,6 +70,11 @@ var dependencies: [Package.Dependency] {
     }
 }
 
+let wasiLibcCSettings: [CSetting] = [
+    .define("_WASI_EMULATED_SIGNAL", .when(platforms: [.wasi])),
+    .define("_WASI_EMULATED_MMAN", .when(platforms: [.wasi])),
+]
+
 let package = Package(
     name: "swift-foundation",
     platforms: [.macOS("13.3"), .iOS("16.4"), .tvOS("16.4"), .watchOS("9.4")],
@@ -80,15 +85,23 @@ let package = Package(
     dependencies: dependencies,
     targets: [
         // _FoundationCShims (Internal)
-        .target(name: "_FoundationCShims",
-                cSettings: [.define("_CRT_SECURE_NO_WARNINGS",
-                                    .when(platforms: [.windows]))]),
+        .target(
+            name: "_FoundationCShims",
+            cSettings: [
+                .define("_CRT_SECURE_NO_WARNINGS", .when(platforms: [.windows]))
+            ] + wasiLibcCSettings
+        ),
 
         // TestSupport (Internal)
-        .target(name: "TestSupport", dependencies: [
-            "FoundationEssentials",
-            "FoundationInternationalization",
-        ], swiftSettings: availabilityMacros + concurrencyChecking),
+        .target(
+            name: "TestSupport",
+            dependencies: [
+                "FoundationEssentials",
+                "FoundationInternationalization",
+            ],
+            cSettings: wasiLibcCSettings,
+            swiftSettings: availabilityMacros + concurrencyChecking
+        ),
 
         // FoundationEssentials
         .target(
@@ -119,11 +132,14 @@ let package = Package(
           ],
           cSettings: [
             .define("_GNU_SOURCE", .when(platforms: [.linux]))
-          ],
+          ] + wasiLibcCSettings,
           swiftSettings: [
             .enableExperimentalFeature("VariadicGenerics"),
             .enableExperimentalFeature("AccessLevelOnImport")
-          ] + availabilityMacros + concurrencyChecking
+          ] + availabilityMacros + concurrencyChecking,
+          linkerSettings: [
+            .linkedLibrary("wasi-emulated-getpid", .when(platforms: [.wasi])),
+          ]
         ),
         .testTarget(
             name: "FoundationEssentialsTests",
@@ -155,6 +171,7 @@ let package = Package(
                 "CMakeLists.txt",
                 "Predicate/CMakeLists.txt"
             ],
+            cSettings: wasiLibcCSettings,
             swiftSettings: [
                 .enableExperimentalFeature("AccessLevelOnImport")
             ] + availabilityMacros + concurrencyChecking
diff --git a/Sources/FoundationEssentials/CMakeLists.txt b/Sources/FoundationEssentials/CMakeLists.txt
index d9ebc2ebb..7cddff682 100644
--- a/Sources/FoundationEssentials/CMakeLists.txt
+++ b/Sources/FoundationEssentials/CMakeLists.txt
@@ -66,6 +66,7 @@ target_compile_options(FoundationEssentials PRIVATE
     "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xfrontend -enable-experimental-feature -Xfrontend StrictConcurrency>"
     "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xfrontend -enable-upcoming-feature -Xfrontend InferSendableFromCaptures>")
 target_compile_options(FoundationEssentials PRIVATE ${_SwiftFoundation_availability_macros})
+target_compile_options(FoundationEssentials PRIVATE ${_SwiftFoundation_wasi_libc_flags})
 target_compile_options(FoundationEssentials PRIVATE -package-name "SwiftFoundation")
 
 target_link_libraries(FoundationEssentials PUBLIC
diff --git a/Sources/FoundationInternationalization/CMakeLists.txt b/Sources/FoundationInternationalization/CMakeLists.txt
index 5a89ceb88..857db9cac 100644
--- a/Sources/FoundationInternationalization/CMakeLists.txt
+++ b/Sources/FoundationInternationalization/CMakeLists.txt
@@ -33,6 +33,7 @@ target_compile_options(FoundationInternationalization PRIVATE
     "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xfrontend -enable-experimental-feature -Xfrontend StrictConcurrency>"
     "SHELL:$<$<COMPILE_LANGUAGE:Swift>:-Xfrontend -enable-upcoming-feature -Xfrontend InferSendableFromCaptures>")
 target_compile_options(FoundationInternationalization PRIVATE ${_SwiftFoundation_availability_macros})
+target_compile_options(FoundationInternationalization PRIVATE ${_SwiftFoundation_wasi_libc_flags})
 target_compile_options(FoundationInternationalization PRIVATE -package-name "SwiftFoundation")
 
 target_link_libraries(FoundationInternationalization PUBLIC
diff --git a/Sources/_FoundationCShims/include/_CStdlib.h b/Sources/_FoundationCShims/include/_CStdlib.h
index 8967eb7f4..03373934b 100644
--- a/Sources/_FoundationCShims/include/_CStdlib.h
+++ b/Sources/_FoundationCShims/include/_CStdlib.h
@@ -60,7 +60,21 @@
 #endif
 
 #if __has_include(<signal.h>)
-#include <signal.h>
+/// Guard against including `signal.h` on WASI. The `signal.h` header file
+/// itself is available in wasi-libc, but it's just a stub that doesn't actually
+/// do anything. And also including it requires a special macro definition
+/// (`_WASI_EMULATED_SIGNAL`) and it causes compilation errors without the macro.
+# if !TARGET_OS_WASI || defined(_WASI_EMULATED_SIGNAL)
+#  include <signal.h>
+# endif
+#endif
+
+#if __has_include(<sys/mman.h>)
+/// Similar to `signal.h`, guard against including `sys/mman.h` on WASI unless
+/// `_WASI_EMULATED_MMAN` is enabled.
+# if !TARGET_OS_WASI || defined(_WASI_EMULATED_MMAN)
+#  include <sys/mman.h>
+# endif
 #endif
 
 #if __has_include(<stdalign.h>)