diff --git a/build/jam/MiscRules b/build/jam/MiscRules
index 8eea5ca2d8..6755a2a4c8 100644
--- a/build/jam/MiscRules
+++ b/build/jam/MiscRules
@@ -210,7 +210,7 @@ rule RunCommandLine commandLine
 actions RunCommandLine1 {
 	target=target;
 	for t in $(2) ; do
-		target+=X
+		target=${target}X
 		eval "${target}=${t}"
 	done
 	$(HOST_ADD_BUILD_COMPATIBILITY_LIB_DIR)