diff --git a/cpufreq/cpufreq_04.sh b/cpufreq/cpufreq_04.sh
index 5b1c508..f044164 100755
--- a/cpufreq/cpufreq_04.sh
+++ b/cpufreq/cpufreq_04.sh
@@ -52,7 +52,7 @@
 fi
 
 supported=$(cat $CPU_PATH/cpu0/cpufreq/scaling_available_governors | grep "userspace")
-if [ -z $supported ]; then
+if [ -z "$supported" ]; then
     log_skip "userspace not supported"
 else
     for_each_cpu for_each_frequency check_frequency || exit 1
diff --git a/cpufreq/cpufreq_05.sh b/cpufreq/cpufreq_05.sh
index ae6b670..f4cc997 100755
--- a/cpufreq/cpufreq_05.sh
+++ b/cpufreq/cpufreq_05.sh
@@ -52,7 +52,7 @@
 }
 
 supported=$(cat $CPU_PATH/cpu0/cpufreq/scaling_available_governors | grep "ondemand")
-if [ -z $supported ]; then
+if [ -z "$supported" ]; then
     log_skip "ondemand not supported"
 else
     for cpu in $(ls $CPU_PATH | grep "cpu[0-9].*"); do
@@ -62,7 +62,7 @@
 fi
 
 supported=$(cat $CPU_PATH/cpu0/cpufreq/scaling_available_governors | grep "conservative")
-if [ -z $supported ]; then
+if [ -z "$supported" ]; then
     log_skip "conservative not supported"
 else
     for cpu in $(ls $CPU_PATH | grep "cpu[0-9].*"); do
@@ -72,7 +72,7 @@
 fi
 
 supported=$(cat $CPU_PATH/cpu0/cpufreq/scaling_available_governors | grep "userspace")
-if [ -z $supported ]; then
+if [ -z "$supported" ]; then
     log_skip "userspace not supported"
 else
     for cpu in $(ls $CPU_PATH | grep "cpu[0-9].*"); do
diff --git a/cpufreq/cpufreq_06.sh b/cpufreq/cpufreq_06.sh
index 215bf61..cb45e4b 100755
--- a/cpufreq/cpufreq_06.sh
+++ b/cpufreq/cpufreq_06.sh
@@ -107,7 +107,7 @@
 fi
 
 supported=$(cat $CPU_PATH/cpu0/cpufreq/scaling_available_governors | grep "userspace")
-if [ -z $supported ]; then
+if [ -z "$supported" ]; then
     log_skip "userspace not supported"
     exit 0
 fi
diff --git a/cpufreq/cpufreq_07.sh b/cpufreq/cpufreq_07.sh
index 539e2d1..354ed46 100755
--- a/cpufreq/cpufreq_07.sh
+++ b/cpufreq/cpufreq_07.sh
@@ -83,7 +83,7 @@
 fi
 
 supported=$(cat $CPU_PATH/cpu0/cpufreq/scaling_available_governors | grep "ondemand")
-if [ -z $supported ]; then
+if [ -z "$supported" ]; then
     log_skip "ondemand not supported"
     exit 0
 fi
diff --git a/cpufreq/cpufreq_08.sh b/cpufreq/cpufreq_08.sh
index e881f72..328b4f5 100755
--- a/cpufreq/cpufreq_08.sh
+++ b/cpufreq/cpufreq_08.sh
@@ -72,7 +72,7 @@
 fi
 
 supported=$(cat $CPU_PATH/cpu0/cpufreq/scaling_available_governors | grep "userspace")
-if [ -z $supported ]; then
+if [ -z "$supported" ]; then
     log_skip "userspace not supported"
     exit 0
 fi
diff --git a/cpufreq/cpufreq_09.sh b/cpufreq/cpufreq_09.sh
index fc700c2..c1d1a7b 100755
--- a/cpufreq/cpufreq_09.sh
+++ b/cpufreq/cpufreq_09.sh
@@ -68,7 +68,7 @@
 fi
 
 supported=$(cat $CPU_PATH/cpu0/cpufreq/scaling_available_governors | grep "powersave")
-if [ -z $supported ]; then
+if [ -z "$supported" ]; then
     log_skip "powersave not supported"
     exit 0
 fi