diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -10234,6 +10234,11 @@
   "%select{non-pointer|function pointer|void pointer}0 argument to "
   "'__builtin_launder' is not allowed">;
 
+def warn_mismatched_import : Warning<
+  "import %select{module|name}0 does not match previous declaration">;
+def warn_import_on_definition : Warning<
+  "import %select{module|name}0 cannot be applied to a function with a definition">;
+
 def err_preserve_field_info_not_field : Error<
   "__builtin_preserve_field_info argument %0 not a field access">;
 def err_preserve_field_info_not_const: Error<
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -2833,6 +2833,10 @@
                                                 const InternalLinkageAttr &AL);
   CommonAttr *mergeCommonAttr(Decl *D, const ParsedAttr &AL);
   CommonAttr *mergeCommonAttr(Decl *D, const CommonAttr &AL);
+  WebAssemblyImportNameAttr *mergeImportNameAttr(
+      Decl *D, const WebAssemblyImportNameAttr &AL);
+  WebAssemblyImportModuleAttr *mergeImportModuleAttr(
+      Decl *D, const WebAssemblyImportModuleAttr &AL);
 
   void mergeDeclAttributes(NamedDecl *New, Decl *Old,
                            AvailabilityMergeKind AMK = AMK_Redeclaration);
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2591,6 +2591,10 @@
     NewAttr = S.mergeSpeculativeLoadHardeningAttr(D, *SLHA);
   else if (const auto *SLHA = dyn_cast<NoSpeculativeLoadHardeningAttr>(Attr))
     NewAttr = S.mergeNoSpeculativeLoadHardeningAttr(D, *SLHA);
+  else if (const auto *IMA = dyn_cast<WebAssemblyImportModuleAttr>(Attr))
+    NewAttr = S.mergeImportModuleAttr(D, *IMA);
+  else if (const auto *INA = dyn_cast<WebAssemblyImportNameAttr>(Attr))
+    NewAttr = S.mergeImportNameAttr(D, *INA);
   else if (Attr->shouldInheritEvenIfAlreadyPresent() || !DeclHasAttr(D, Attr))
     NewAttr = cast<InheritableAttr>(Attr->clone(S.Context));
 
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -5776,45 +5776,73 @@
   D->addAttr(UsedAttr::CreateImplicit(S.Context));
 }
 
-static void handleWebAssemblyImportModuleAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
-  if (!isFunctionOrMethod(D)) {
-    S.Diag(D->getLocation(), diag::warn_attribute_wrong_decl_type)
-        << "'import_module'" << ExpectedFunction;
-    return;
+WebAssemblyImportModuleAttr *
+Sema::mergeImportModuleAttr(Decl *D, const WebAssemblyImportModuleAttr &AL) {
+  auto *FD = cast<FunctionDecl>(D);
+
+  if (const auto *ExistingAttr = FD->getAttr<WebAssemblyImportModuleAttr>()) {
+    if (ExistingAttr->getImportModule() == AL.getImportModule())
+      return nullptr;
+    Diag(ExistingAttr->getLocation(), diag::warn_mismatched_import) << 0;
+    Diag(AL.getLoc(), diag::note_previous_attribute);
+    return nullptr;
+  }
+  if (FD->hasBody()) {
+    Diag(AL.getLoc(), diag::warn_import_on_definition) << 0;
+    return nullptr;
   }
+  return ::new (Context) WebAssemblyImportModuleAttr(Context, AL,
+                                                     AL.getImportModule());
+}
 
+WebAssemblyImportNameAttr *
+Sema::mergeImportNameAttr(Decl *D, const WebAssemblyImportNameAttr &AL) {
   auto *FD = cast<FunctionDecl>(D);
-  if (FD->isThisDeclarationADefinition()) {
-    S.Diag(D->getLocation(), diag::err_alias_is_definition) << FD << 0;
-    return;
+
+  if (const auto *ExistingAttr = FD->getAttr<WebAssemblyImportNameAttr>()) {
+    if (ExistingAttr->getImportName() == AL.getImportName())
+      return nullptr;
+    Diag(ExistingAttr->getLocation(), diag::warn_mismatched_import) << 1;
+    Diag(AL.getLoc(), diag::note_previous_attribute);
+    return nullptr;
+  }
+  if (FD->hasBody()) {
+    Diag(AL.getLoc(), diag::warn_import_on_definition) << 1;
+    return nullptr;
   }
+  return ::new (Context) WebAssemblyImportNameAttr(Context, AL,
+                                                   AL.getImportName());
+}
+
+static void
+handleWebAssemblyImportModuleAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
+  auto *FD = cast<FunctionDecl>(D);
 
   StringRef Str;
   SourceLocation ArgLoc;
   if (!S.checkStringLiteralArgumentAttr(AL, 0, Str, &ArgLoc))
     return;
+  if (FD->hasBody()) {
+    S.Diag(AL.getLoc(), diag::warn_import_on_definition) << 0;
+    return;
+  }
 
   FD->addAttr(::new (S.Context)
                   WebAssemblyImportModuleAttr(S.Context, AL, Str));
 }
 
-static void handleWebAssemblyImportNameAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
-  if (!isFunctionOrMethod(D)) {
-    S.Diag(D->getLocation(), diag::warn_attribute_wrong_decl_type)
-        << "'import_name'" << ExpectedFunction;
-    return;
-  }
-
+static void
+handleWebAssemblyImportNameAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   auto *FD = cast<FunctionDecl>(D);
-  if (FD->isThisDeclarationADefinition()) {
-    S.Diag(D->getLocation(), diag::err_alias_is_definition) << FD << 0;
-    return;
-  }
 
   StringRef Str;
   SourceLocation ArgLoc;
   if (!S.checkStringLiteralArgumentAttr(AL, 0, Str, &ArgLoc))
     return;
+  if (FD->hasBody()) {
+    S.Diag(AL.getLoc(), diag::warn_import_on_definition) << 1;
+    return;
+  }
 
   FD->addAttr(::new (S.Context) WebAssemblyImportNameAttr(S.Context, AL, Str));
 }
diff --git a/clang/test/Sema/attr-wasm.c b/clang/test/Sema/attr-wasm.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Sema/attr-wasm.c
@@ -0,0 +1,31 @@
+// RUN: %clang_cc1 -triple wasm32-unknown-unknown -fsyntax-only -verify %s
+
+void name_a() __attribute__((import_name)); //expected-error {{'import_name' attribute takes one argument}}
+
+int name_b __attribute__((import_name("foo"))); //expected-error {{'import_name' attribute only applies to functions}}
+
+void name_c() __attribute__((import_name("foo", "bar"))); //expected-error {{'import_name' attribute takes one argument}}
+
+void name_d() __attribute__((import_name("foo", "bar", "qux"))); //expected-error {{'import_name' attribute takes one argument}}
+
+__attribute__((import_name("foo"))) void name_e() {} //FIXME-expected-error {{import name cannot be applied to a function with a definition}}
+
+void name_z() __attribute__((import_name("foo"))); //expected-note {{previous attribute is here}}
+
+void name_z() __attribute__((import_name("bar"))); //expected-warning {{import name does not match previous declaration}}
+
+void module_a() __attribute__((import_module)); //expected-error {{'import_module' attribute takes one argument}}
+
+int module_b __attribute__((import_module("foo"))); //expected-error {{'import_module' attribute only applies to functions}}
+
+void module_c() __attribute__((import_module("foo", "bar"))); //expected-error {{'import_module' attribute takes one argument}}
+
+void module_d() __attribute__((import_module("foo", "bar", "qux"))); //expected-error {{'import_module' attribute takes one argument}}
+
+void module_e() __attribute__((import_module("foo"))) {} //FIXME-expected-error {{import module cannot be applied to a function with a definition}}
+
+void module_z() __attribute__((import_module("foo"))); //expected-note {{previous attribute is here}}
+
+void module_z() __attribute__((import_module("bar"))); //expected-warning {{import module does not match previous declaration}}
+
+void both() __attribute__((import_name("foo"), import_module("bar")));