diff --git a/lib/ClangImporter/ClangImporter.cpp b/lib/ClangImporter/ClangImporter.cpp
index 3ebdc3ee4f279..c82af4b32686d 100644
--- a/lib/ClangImporter/ClangImporter.cpp
+++ b/lib/ClangImporter/ClangImporter.cpp
@@ -663,10 +663,6 @@ importer::getNormalInvocationArguments(
     }
 
     if (triple.isOSWASI()) {
-      invocationArgStrs.insert(invocationArgStrs.end(),
-                               {"-D_WASI_EMULATED_MMAN",
-                                "-D_WASI_EMULATED_SIGNAL",
-                                "-D_WASI_EMULATED_PROCESS_CLOCKS"});
       SmallString<128> buffer;
       if (auto path = getWasiLibcModuleMapPath(searchPathOpts, triple, buffer)) {
         invocationArgStrs.push_back((Twine("-fmodule-map-file=") + *path).str());
diff --git a/stdlib/public/Platform/SwiftWASILibc.h.gyb b/stdlib/public/Platform/SwiftWASILibc.h.gyb
index 86fc25b24c833..c051627f2b7c0 100644
--- a/stdlib/public/Platform/SwiftWASILibc.h.gyb
+++ b/stdlib/public/Platform/SwiftWASILibc.h.gyb
@@ -105,6 +105,20 @@ headers = [
 ]
 }%
 
+// FIXME?(katei):
+// Those emulations are now enabled by default to have compatibility
+// with other platforms as much as possible without any extra modification.
+// But we should consider moving them into their own submodules.
+#ifndef _WASI_EMULATED_MMAN
+#  define _WASI_EMULATED_MMAN
+#endif
+#ifndef _WASI_EMULATED_SIGNAL
+#  define _WASI_EMULATED_SIGNAL
+#endif
+#ifndef _WASI_EMULATED_PROCESS_CLOCKS
+#  define _WASI_EMULATED_PROCESS_CLOCKS
+#endif
+
 % for header in headers:
 #if __has_include(<${header}>)
 #include <${header}>