diff --git a/lib/Basic/Targets/WebAssembly.cpp b/lib/Basic/Targets/WebAssembly.cpp
index b16442b99b6..78402153a7c 100644
--- a/lib/Basic/Targets/WebAssembly.cpp
+++ b/lib/Basic/Targets/WebAssembly.cpp
@@ -60,6 +60,10 @@ void WebAssemblyTargetInfo::fillValidCPUList(
 void WebAssemblyTargetInfo::getTargetDefines(const LangOptions &Opts,
                                              MacroBuilder &Builder) const {
   defineCPUMacros(Builder, "wasm", /*Tuning=*/false);
+  // HACK: too lazy to backport the WASI target here
+  Builder.defineMacro("__wasi__");
+  // HACK: globally enable WASI mmap emulation
+  Builder.defineMacro("_WASI_EMULATED_MMAN");
   if (SIMDLevel >= SIMD128)
     Builder.defineMacro("__wasm_simd128__");
   if (SIMDLevel >= UnimplementedSIMD128)
diff --git a/lib/Basic/Targets/WebAssembly.h b/lib/Basic/Targets/WebAssembly.h
index 9665156b143..55d90db267e 100644
--- a/lib/Basic/Targets/WebAssembly.h
+++ b/lib/Basic/Targets/WebAssembly.h
@@ -114,6 +114,16 @@ class LLVM_LIBRARY_VISIBILITY WebAssemblyTargetInfo : public TargetInfo {
                ? (IsSigned ? SignedLongLong : UnsignedLongLong)
                : TargetInfo::getLeastIntTypeByWidth(BitWidth, IsSigned);
   }
+
+  CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {
+    switch (CC) {
+    case CC_C:
+    case CC_Swift:
+      return CCCR_OK;
+    default:
+      return CCCR_Warning;
+    }
+  }
 };
 class LLVM_LIBRARY_VISIBILITY WebAssembly32TargetInfo
     : public WebAssemblyTargetInfo {
diff --git a/lib/Driver/ToolChains/Clang.cpp b/lib/Driver/ToolChains/Clang.cpp
index a126b764dea..8cb8760eabe 100644
--- a/lib/Driver/ToolChains/Clang.cpp
+++ b/lib/Driver/ToolChains/Clang.cpp
@@ -448,6 +448,9 @@ static void addExceptionArgs(const ArgList &Args, types::ID InputType,
     // Disable C++ EH by default on XCore and PS4.
     bool CXXExceptionsEnabled =
         Triple.getArch() != llvm::Triple::xcore && !Triple.isPS4CPU();
+    // WebAssembly: no exception handling on WASI
+    if (Triple.isOSBinFormatWasm())
+      CXXExceptionsEnabled = false;
     Arg *ExceptionArg = Args.getLastArg(
         options::OPT_fcxx_exceptions, options::OPT_fno_cxx_exceptions,
         options::OPT_fexceptions, options::OPT_fno_exceptions);