diff --git a/arch/x86_64/tools/mpimcexec.in b/arch/x86_64/tools/mpimcexec.in
index 972d6217..04595f02 100755
--- a/arch/x86_64/tools/mpimcexec.in
+++ b/arch/x86_64/tools/mpimcexec.in
@@ -120,7 +120,7 @@ if [ -z ${RANKS} ] && [ -z ${NODES} ]; then
 	help_exit
 fi
 
-if [ x${COMMAND} = x ]; then
+if [ "x${COMMAND}" = "x" ]; then
 	echo "error: please specify command"
 	help_exit
 fi