diff --git a/tslang/lib/TypeScript/MLIRGenImpl.h b/tslang/lib/TypeScript/MLIRGenImpl.h
index 63aac409e..1c01ddf16 100644
--- a/tslang/lib/TypeScript/MLIRGenImpl.h
+++ b/tslang/lib/TypeScript/MLIRGenImpl.h
@@ -60,6 +60,7 @@
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/raw_ostream.h"
 //#include "llvm/IR/DebugInfoMetadata.h"
@@ -13899,6 +13900,11 @@ class MLIRGenImpl
     }    
 
     // The file an `import` of a local source module names: next to the main file, `.ts` added.
+    // Without an extension, the module's file for the target comes first: `import "./m"` is m.win32.ts
+    // on Windows, m.linux.ts on Linux and Android, m.<the triple's OS name>.ts elsewhere, when it
+    // exists, else m.ts. A module with code per target (the vtables and layouts of a C++ ABI, say)
+    // is then picked as the default library picks lib.win32.ts or lib.linux.ts, while the importer
+    // names one module.
     std::string includeFilePath(StringRef fileName)
     {
         SmallString<256> fileNameStr(fileName);
@@ -13910,11 +13916,6 @@ class MLIRGenImpl
             fileNameStr.append(subStr);
         }
 
-        if (sys::path::extension(fileName) == "")
-        {
-            fileNameStr += ".ts";
-        }
-
         SmallString<256> fullPath;
 
         if (!sys::path::has_root_path(fileNameStr)) {
@@ -13924,9 +13925,40 @@ class MLIRGenImpl
         }
 
         sys::path::append(fullPath, fileNameStr);
+
+        if (sys::path::extension(fileName) == "")
+        {
+            SmallString<256> targetPath(fullPath);
+            targetPath += ".";
+            targetPath += targetOSFileSuffix();
+            targetPath += ".ts";
+            if (sys::fs::exists(targetPath))
+            {
+                return targetPath.str().str();
+            }
+
+            fullPath += ".ts";
+        }
+
         return fullPath.str().str();
     }
 
+    // The OS part of a module's file name for the target (includeFilePath): win32, linux (Android
+    // too, as the default library builds lib.linux.ts for it), or the target triple's OS name.
+    StringRef targetOSFileSuffix()
+    {
+        llvm::Triple triple(compileOptions.moduleTargetTriple);
+        switch (triple.getOS())
+        {
+        case llvm::Triple::Win32:
+            return "win32";
+        case llvm::Triple::Linux:
+            return "linux";
+        default:
+            return llvm::Triple::getOSTypeName(triple.getOS());
+        }
+    }
+
     std::pair<SourceFile, std::vector<SourceFile>> loadIncludeFile(mlir::Location location, StringRef fullPath)
     {
         std::string ignored;
diff --git a/tslang/test/tester/CMakeLists.txt b/tslang/test/tester/CMakeLists.txt
index e8302c4b6..11694dce5 100644
--- a/tslang/test/tester/CMakeLists.txt
+++ b/tslang/test/tester/CMakeLists.txt
@@ -1340,6 +1340,27 @@ tslang_add_test(NAME test-compile-export-import-owned-returns COMMAND test-runne
 tslang_add_test(NAME test-compile-export-import-const-locals COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/import_const_locals.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_const_locals.ts")
 tslang_add_test(NAME test-compile-export-import-const-functions COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/import_const_functions.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_const_functions.ts")
 tslang_add_test(NAME test-compile-export-import-generators COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/import_generators.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_generators.ts")
+# `import './export_os_suffix'` takes the target's file, export_os_suffix.win32.ts or
+# export_os_suffix.linux.ts: the host's is compiled and linked beside it, and the import's
+# declarations for each target are those of its file (the OS function that file declares).
+if (WIN32)
+    tslang_add_test(NAME test-compile-export-import-os-suffix COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/import_os_suffix.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_os_suffix.win32.ts")
+elseif (CMAKE_SYSTEM_NAME STREQUAL "Linux")
+    tslang_add_test(NAME test-compile-export-import-os-suffix COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/import_os_suffix.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_os_suffix.linux.ts")
+endif()
+foreach(os_suffix "win32|x86_64-pc-windows-msvc|GetCurrentProcessId|getpid" "linux|x86_64-unknown-linux-gnu|getpid|GetCurrentProcessId")
+    string(REPLACE "|" ";" os_suffix "${os_suffix}")
+    list(GET os_suffix 0 os_name)
+    list(GET os_suffix 1 os_triple)
+    list(GET os_suffix 2 os_function)
+    list(GET os_suffix 3 os_other_function)
+    add_test(NAME test-compile-import-os-suffix-${os_name}
+             COMMAND $<TARGET_FILE:tslang> --emit=mlir --no-default-lib -mtriple=${os_triple}
+                     "${PROJECT_SOURCE_DIR}/test/tester/tests/import_os_suffix.ts")
+    set_tests_properties(test-compile-import-os-suffix-${os_name}
+                         PROPERTIES PASS_REGULAR_EXPRESSION "ts\\.Func @${os_function} "
+                                    FAIL_REGULAR_EXPRESSION "ts\\.Func @${os_other_function} |error:")
+endforeach()
 tslang_add_test(NAME test-compile-rc-export-import-owned-returns COMMAND test-runner -mm=rc "${PROJECT_SOURCE_DIR}/test/tester/tests/import_owned_returns.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_owned_returns.ts")
 tslang_add_test(NAME test-compile-none-export-import-owned-returns COMMAND test-runner -mm=none "${PROJECT_SOURCE_DIR}/test/tester/tests/import_owned_returns.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_owned_returns.ts")
 tslang_add_test(NAME test-compile-export-import-class-extends COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/import_class_extends.ts" "${PROJECT_SOURCE_DIR}/test/tester/tests/export_class_extends.ts")
diff --git a/tslang/test/tester/tests/export_os_suffix.linux.ts b/tslang/test/tester/tests/export_os_suffix.linux.ts
new file mode 100644
index 000000000..3288a7819
--- /dev/null
+++ b/tslang/test/tester/tests/export_os_suffix.linux.ts
@@ -0,0 +1,13 @@
+// The Linux file of the module `import './export_os_suffix'` names (import_os_suffix.ts): an
+// import without an extension takes <name>.win32.ts on Windows, <name>.linux.ts on Linux.
+
+declare function getpid(): s32;
+
+namespace O {
+
+    export const osFile = "linux";
+
+    export function processId(): u32 {
+        return <u32>getpid();
+    }
+}
diff --git a/tslang/test/tester/tests/export_os_suffix.win32.ts b/tslang/test/tester/tests/export_os_suffix.win32.ts
new file mode 100644
index 000000000..6da3ecbbf
--- /dev/null
+++ b/tslang/test/tester/tests/export_os_suffix.win32.ts
@@ -0,0 +1,13 @@
+// The Windows file of the module `import './export_os_suffix'` names (import_os_suffix.ts): an
+// import without an extension takes <name>.win32.ts on Windows, <name>.linux.ts on Linux.
+
+declare function GetCurrentProcessId(): u32;
+
+namespace O {
+
+    export const osFile = "win32";
+
+    export function processId(): u32 {
+        return GetCurrentProcessId();
+    }
+}
diff --git a/tslang/test/tester/tests/import_os_suffix.ts b/tslang/test/tester/tests/import_os_suffix.ts
new file mode 100644
index 000000000..d6e2f65f3
--- /dev/null
+++ b/tslang/test/tester/tests/import_os_suffix.ts
@@ -0,0 +1,12 @@
+import './export_os_suffix'
+
+// There is no export_os_suffix.ts: the import takes the target's file, export_os_suffix.win32.ts or
+// export_os_suffix.linux.ts, the one compiled and linked beside this (the other one's functions
+// would be missing at link time).
+
+function main() {
+    assert(O.osFile == "win32" || O.osFile == "linux", "the module's file for the target");
+    assert(O.processId() != 0, "and its functions");
+
+    print("done.");
+}