Index: include/llvm/ExecutionEngine/Orc/Legacy.h
===================================================================
--- include/llvm/ExecutionEngine/Orc/Legacy.h
+++ include/llvm/ExecutionEngine/Orc/Legacy.h
@@ -125,6 +125,11 @@
         Result.insert(S);
     } else if (auto Err = Sym.takeError())
       return std::move(Err);
+    else {
+      // If there is no existing definition then the caller is responsible for
+      // it.
+      Result.insert(S);
+    }
   }
 
   return Result;
Index: unittests/ExecutionEngine/Orc/LegacyAPIInteropTest.cpp
===================================================================
--- unittests/ExecutionEngine/Orc/LegacyAPIInteropTest.cpp
+++ unittests/ExecutionEngine/Orc/LegacyAPIInteropTest.cpp
@@ -94,7 +94,7 @@
       getResponsibilitySetWithLegacyFn(SymbolNameSet({Bar, Baz}), LegacyLookup);
 
   EXPECT_TRUE(!!RS) << "Expected getResponsibilitySetWithLegacyFn to succeed";
-  EXPECT_EQ(RS->size(), 1U) << "Wrong number of symbols returned";
+  EXPECT_EQ(RS->size(), 2U) << "Wrong number of symbols returned";
   EXPECT_EQ(RS->count(Bar), 1U) << "Incorrect responsibility set returned";
   EXPECT_FALSE(BarMaterialized)
       << "lookupFlags should not have materialized bar";