diff --git a/llvm/include/llvm/Support/Error.h b/llvm/include/llvm/Support/Error.h
--- a/llvm/include/llvm/Support/Error.h
+++ b/llvm/include/llvm/Support/Error.h
@@ -704,6 +704,12 @@
   if (Err) {
     if (!Msg)
       Msg = "Failure value returned from cantFail wrapped call";
+#ifndef NDEBUG
+    std::string Str;
+    raw_string_ostream OS(Str);
+    OS << Msg << "\n" << Err;
+    Msg = OS.str().c_str();
+#endif
     llvm_unreachable(Msg);
   }
 }
@@ -728,6 +734,13 @@
   else {
     if (!Msg)
       Msg = "Failure value returned from cantFail wrapped call";
+#ifndef NDEBUG
+    std::string Str;
+    raw_string_ostream OS(Str);
+    auto E = ValOrErr.takeError();
+    OS << Msg << "\n" << E;
+    Msg = OS.str().c_str();
+#endif
     llvm_unreachable(Msg);
   }
 }
@@ -752,6 +765,13 @@
   else {
     if (!Msg)
       Msg = "Failure value returned from cantFail wrapped call";
+#ifndef NDEBUG
+    std::string Str;
+    raw_string_ostream OS(Str);
+    auto E = ValOrErr.takeError();
+    OS << Msg << "\n" << E;
+    Msg = OS.str().c_str();
+#endif
     llvm_unreachable(Msg);
   }
 }
diff --git a/llvm/unittests/Support/ErrorTest.cpp b/llvm/unittests/Support/ErrorTest.cpp
--- a/llvm/unittests/Support/ErrorTest.cpp
+++ b/llvm/unittests/Support/ErrorTest.cpp
@@ -390,7 +390,8 @@
   };
 
   EXPECT_DEATH(FailToHandle(),
-               "Failure value returned from cantFail wrapped call")
+               "Failure value returned from cantFail wrapped call\n"
+               "CustomError \\{7\\}")
       << "Unhandled Error in handleAllErrors call did not cause an "
          "abort()";
 }
@@ -409,7 +410,8 @@
   };
 
   EXPECT_DEATH(ReturnErrorFromHandler(),
-               "Failure value returned from cantFail wrapped call")
+               "Failure value returned from cantFail wrapped call\n"
+               "CustomError \\{7\\}")
       << " Error returned from handler in handleAllErrors call did not "
          "cause abort()";
 }
@@ -510,11 +512,12 @@
 // Test that cantFail results in a crash if you pass it a failure value.
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS && !defined(NDEBUG)
 TEST(Error, CantFailDeath) {
-  EXPECT_DEATH(
-      cantFail(make_error<StringError>("foo", inconvertibleErrorCode()),
-               "Cantfail call failed"),
-      "Cantfail call failed")
-    << "cantFail(Error) did not cause an abort for failure value";
+  EXPECT_DEATH(cantFail(make_error<StringError>("Original error message",
+                                                inconvertibleErrorCode()),
+                        "Cantfail call failed"),
+               "Cantfail call failed\n"
+               "Original error message")
+      << "cantFail(Error) did not cause an abort for failure value";
 
   EXPECT_DEATH(
       {