diff --git a/Source/cmAddCustomCommandCommand.cxx b/Source/cmAddCustomCommandCommand.cxx
index 2c4a4ca91..2e284989b 100644
--- a/Source/cmAddCustomCommandCommand.cxx
+++ b/Source/cmAddCustomCommandCommand.cxx
@@ -263,8 +263,8 @@ bool cmAddCustomCommandCommand::InitialPass(
 
     // No command for this output exists.
     std::ostringstream e;
-    e << "given APPEND option with output \"" << output[0]
-      << "\" which is not already a custom command output.";
+    e << "given APPEND option with output\n\"" << output[0]
+      << "\"\nwhich is not already a custom command output.";
     this->SetError(e.str());
     return false;
   }
diff --git a/Tests/RunCMake/add_custom_command/AppendNotOutput-stderr.txt b/Tests/RunCMake/add_custom_command/AppendNotOutput-stderr.txt
index 96d097228..cd542d875 100644
--- a/Tests/RunCMake/add_custom_command/AppendNotOutput-stderr.txt
+++ b/Tests/RunCMake/add_custom_command/AppendNotOutput-stderr.txt
@@ -1,5 +1,8 @@
 CMake Error at AppendNotOutput.cmake:1 \(add_custom_command\):
-  add_custom_command given APPEND option with output.*
+  add_custom_command given APPEND option with output
+
+  .*RunCMake/add_custom_command/AppendNotOutput-build/out.*
+
   which is not already a custom command output.
 Call Stack \(most recent call first\):
   CMakeLists.txt:3 \(include\)