diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -3348,8 +3348,8 @@
 /// an externally visible symbol, but "extern inline" will not create an
 /// externally visible symbol.
 bool FunctionDecl::isInlineDefinitionExternallyVisible() const {
-  assert((doesThisDeclarationHaveABody() || willHaveBody()) &&
-         "Must be a function definition");
+  assert((doesThisDeclarationHaveABody() || willHaveBody()) ||
+         hasAttr<AliasAttr>() && "Must be a function definition");
   assert(isInlined() && "Function must be inline");
   ASTContext &Context = getASTContext();
 
diff --git a/clang/test/CodeGen/alias.c b/clang/test/CodeGen/alias.c
--- a/clang/test/CodeGen/alias.c
+++ b/clang/test/CodeGen/alias.c
@@ -99,3 +99,8 @@
 // CHECKGLOBALS-NOT: @test11_foo = dso_local
 void test11(void) {}
 static void test11_foo(void) __attribute__((alias("test11")));
+
+// Test that gnu_inline+alias work.
+// CHECKGLOBALS: @test12_alias = alias void (), void ()* @test12
+void test12(void) {}
+inline void test12_alias(void) __attribute__((gnu_inline, alias("test12")));