diff --git a/include/llvm/ExecutionEngine/Orc/Layer.h b/include/llvm/ExecutionEngine/Orc/Layer.h
index 18dd4573119..ed839b518b7 100644
--- a/include/llvm/ExecutionEngine/Orc/Layer.h
+++ b/include/llvm/ExecutionEngine/Orc/Layer.h
@@ -63,11 +63,10 @@ public:
 
 protected:
   std::unique_ptr<Module> M;
+  std::map<SymbolStringPtr, GlobalValue *> SymbolToDefinition;
 
 private:
   void discard(const VSO &V, SymbolStringPtr Name) override;
-
-  std::map<SymbolStringPtr, GlobalValue *> Discardable;
 };
 
 /// MaterializationUnit that materializes modules by calling the 'emit' method
diff --git a/lib/ExecutionEngine/Orc/Layer.cpp b/lib/ExecutionEngine/Orc/Layer.cpp
index 346dde4f7a8..1927bce45d4 100644
--- a/lib/ExecutionEngine/Orc/Layer.cpp
+++ b/lib/ExecutionEngine/Orc/Layer.cpp
@@ -46,17 +46,19 @@ IRMaterializationUnit::IRMaterializationUnit(ExecutionSession &ES,
         !G.hasAvailableExternallyLinkage()) {
       auto MangledName = Mangle(G.getName());
       SymbolFlags[MangledName] = JITSymbolFlags::fromGlobalValue(G);
-      Discardable[MangledName] = &G;
+      SymbolToDefinition[MangledName] = &G;
     }
   }
 }
 
 void IRMaterializationUnit::discard(const VSO &V, SymbolStringPtr Name) {
-  auto I = Discardable.find(Name);
-  assert(I != Discardable.end() &&
+  auto I = SymbolToDefinition.find(Name);
+  assert(I != SymbolToDefinition.end() &&
          "Symbol not provided by this MU, or previously discarded");
+  assert(!I->second->isDeclaration() &&
+         "Discard should only apply to definitions");
   I->second->setLinkage(GlobalValue::AvailableExternallyLinkage);
-  Discardable.erase(I);
+  SymbolToDefinition.erase(I);
 }
 
 BasicIRLayerMaterializationUnit::BasicIRLayerMaterializationUnit(