Index: lib/IR/Core.cpp
===================================================================
--- lib/IR/Core.cpp
+++ lib/IR/Core.cpp
@@ -563,9 +563,23 @@
   return nullptr;
 }
 
-void LLVMSetMetadata(LLVMValueRef Inst, unsigned KindID, LLVMValueRef MD) {
-  MDNode *N =
-      MD ? cast<MDNode>(unwrap<MetadataAsValue>(MD)->getMetadata()) : nullptr;
+// MetadataAsValue uses a canonical format which strips the actual MDNode for
+// MDNode with just a single constant value, storing just a ConstantAsMetadata
+// This undoes this canonicalization, reconstructing the MDNode.
+static MDNode *extractMDNode(MetadataAsValue *MAV) {
+  Metadata *MD = MAV->getMetadata();
+  assert((isa<MDNode>(MD) || isa<ConstantAsMetadata>(MD)) &&
+      "Expected a metadata node or a canonicalized constant");
+
+  if (MDNode *N = dyn_cast<MDNode>(MD))
+    return N;
+
+  return MDNode::get(MAV->getContext(), MD);
+}
+
+void LLVMSetMetadata(LLVMValueRef Inst, unsigned KindID, LLVMValueRef Val) {
+  MDNode *N = Val ? extractMDNode(unwrap<MetadataAsValue>(Val)) : nullptr;
+
   unwrap<Instruction>(Inst)->setMetadata(KindID, N);
 }
 
@@ -795,7 +809,7 @@
     return;
   if (!Val)
     return;
-  N->addOperand(cast<MDNode>(unwrap<MetadataAsValue>(Val)->getMetadata()));
+  N->addOperand(extractMDNode(unwrap<MetadataAsValue>(Val)));
 }
 
 /*--.. Operations on scalar constants ......................................--*/
Index: test/Bindings/llvm-c/add_named_metadata_operand.ll
===================================================================
--- /dev/null
+++ test/Bindings/llvm-c/add_named_metadata_operand.ll
@@ -0,0 +1,2 @@
+; RUN: llvm-c-test --add-named-metadata-operand < /dev/null
+; This used to trigger an assertion
Index: test/Bindings/llvm-c/set_metadata.ll
===================================================================
--- /dev/null
+++ test/Bindings/llvm-c/set_metadata.ll
@@ -0,0 +1,2 @@
+; RUN: llvm-c-test --set-metadata < /dev/null
+; This used to trigger an assertion
Index: tools/llvm-c-test/CMakeLists.txt
===================================================================
--- tools/llvm-c-test/CMakeLists.txt
+++ tools/llvm-c-test/CMakeLists.txt
@@ -41,6 +41,7 @@
   include-all.c
   main.c
   module.c
+  metadata.c
   object.c
   targets.c
   )
Index: tools/llvm-c-test/llvm-c-test.h
===================================================================
--- tools/llvm-c-test/llvm-c-test.h
+++ tools/llvm-c-test/llvm-c-test.h
@@ -27,6 +27,10 @@
 // disassemble.c
 int disassemble(void);
 
+// metadata.c
+int add_named_metadata_operand(void);
+int set_metadata(void);
+
 // object.c
 int object_list_sections(void);
 int object_list_symbols(void);
Index: tools/llvm-c-test/main.c
===================================================================
--- tools/llvm-c-test/main.c
+++ tools/llvm-c-test/main.c
@@ -65,6 +65,10 @@
     return disassemble();
   } else if (argc == 2 && !strcmp(argv[1], "--calc")) {
     return calc();
+  } else if (argc == 2 && !strcmp(argv[1], "--add-named-metadata-operand")) {
+    return add_named_metadata_operand();
+  } else if (argc == 2 && !strcmp(argv[1], "--set-metadata")) {
+    return set_metadata();
   } else {
     print_usage();
   }
Index: tools/llvm-c-test/metadata.c
===================================================================
--- tools/llvm-c-test/metadata.c
+++ tools/llvm-c-test/metadata.c
@@ -1,4 +1,4 @@
-/*===-- llvm-c-test.h - tool for testing libLLVM and llvm-c API -----------===*\
+/*===-- object.c - tool for testing libLLVM and llvm-c API ----------------===*\
 |*                                                                            *|
 |*                     The LLVM Compiler Infrastructure                       *|
 |*                                                                            *|
@@ -7,31 +7,32 @@
 |*                                                                            *|
 |*===----------------------------------------------------------------------===*|
 |*                                                                            *|
-|* Header file for llvm-c-test                                                *|
+|* This file implements the --set-metadata command in llvm-c-test.            *|
 |*                                                                            *|
 \*===----------------------------------------------------------------------===*/
-#ifndef LLVM_C_TEST_H
-#define LLVM_C_TEST_H
 
-// helpers.c
-void tokenize_stdin(void (*cb)(char **tokens, int ntokens));
+#include "llvm-c-test.h"
+#include "llvm-c/Core.h"
 
-// module.c
-int module_dump(void);
-int module_list_functions(void);
-int module_list_globals(void);
+int add_named_metadata_operand(void) {
+  LLVMModuleRef m = LLVMModuleCreateWithName("Mod");
+  LLVMValueRef values[] = { LLVMConstInt(LLVMInt32Type(), 0, 0) };
 
-// calc.c
-int calc(void);
+  // This used to trigger an assertion
+  LLVMAddNamedMetadataOperand(m, "name", LLVMMDNode(values, 1));
 
-// disassemble.c
-int disassemble(void);
+  return 0;
+}
 
-// object.c
-int object_list_sections(void);
-int object_list_symbols(void);
+int set_metadata(void) {
+  LLVMBuilderRef b = LLVMCreateBuilder();
+  LLVMValueRef values[] = { LLVMConstInt(LLVMInt32Type(), 0, 0) };
 
-// targets.c
-int targets_list(void);
+  // This used to trigger an assertion
+  LLVMSetMetadata(
+      LLVMBuildRetVoid(b),
+      LLVMGetMDKindID("kind", 4),
+      LLVMMDNode(values, 1));
 
-#endif
+  return 0;
+}