diff --git a/llvm/include/llvm-c/Core.h b/llvm/include/llvm-c/Core.h
--- a/llvm/include/llvm-c/Core.h
+++ b/llvm/include/llvm-c/Core.h
@@ -810,6 +810,15 @@
                        const char *Key, size_t KeyLen,
                        LLVMMetadataRef Val);
 
+/**
+ * Add a module-level flag to the module-level flags metadata if it doesn't
+ * already exist.
+ *
+ * @see Module::addModuleFlag()
+ */
+void LLVMAddRawModuleFlag(LLVMModuleRef M, LLVMModuleFlagBehavior,
+                          const char *Key, size_t KeyLen, int32_t Val);
+
 /**
  * Dump a representation of a module to stderr.
  *
diff --git a/llvm/lib/IR/Core.cpp b/llvm/lib/IR/Core.cpp
--- a/llvm/lib/IR/Core.cpp
+++ b/llvm/lib/IR/Core.cpp
@@ -386,6 +386,12 @@
                            {Key, KeyLen}, unwrap(Val));
 }
 
+void LLVMAddRawModuleFlag(LLVMModuleRef M, LLVMModuleFlagBehavior Behavior,
+                          const char *Key, size_t KeyLen, int32_t Val) {
+  unwrap(M)->addModuleFlag(map_to_llvmModFlagBehavior(Behavior), {Key, KeyLen},
+                           Val);
+}
+
 /*--.. Printing modules ....................................................--*/
 
 void LLVMDumpModule(LLVMModuleRef M) {