diff --git a/TOOLS/checktree.sh b/TOOLS/checktree.sh
index 80231c207e..a603efb4ca 100755
--- a/TOOLS/checktree.sh
+++ b/TOOLS/checktree.sh
@@ -363,37 +363,37 @@ if [ "$_stupid" = "yes" -a -n "$chfilelist" ]; then
     for i in calloc malloc realloc memalign av_malloc av_mallocz faad_malloc \
              lzo_malloc safe_malloc mpeg2_malloc _ogg_malloc; do
         printhead "--> casting of void* $i()"
-        grep $_grepopts "([ 	]*[a-zA-Z_]\+[ 	]*\*.*)[ 	]*$i" $chfilelist
+        grep $_grepopts "([ $TAB]*[a-zA-Z_]\+[ $TAB]*\*.*)[ $TAB]*$i" $chfilelist
     done
 
     for i in "" signed unsigned; do
         printhead "--> usage of sizeof($i char)"
-        grep $_grepopts "sizeof[ 	]*([ 	]*$i[ 	]*char[ 	]*)" $chfilelist
+        grep $_grepopts "sizeof[ $TAB]*([ $TAB]*$i[ $TAB]*char[ $TAB]*)" $chfilelist
     done
 
     for i in int8_t uint8_t; do
         printhead "--> usage of sizeof($i)"
-        grep $_grepopts "sizeof[ 	]*([ 	]*$i[ 	]*)" $chfilelist
+        grep $_grepopts "sizeof[ $TAB]*([ $TAB]*$i[ $TAB]*)" $chfilelist
     done
 
     printhead "--> usage of &&1"
-    grep $_grepopts "&&[ 	]*1" $chfilelist
+    grep $_grepopts "&&[ $TAB]*1" $chfilelist
 
     printhead "--> usage of ||0"
-    grep $_grepopts "||[ 	]*0" $chfilelist
+    grep $_grepopts "||[ $TAB]*0" $chfilelist
 
     # added a-fA-F_ to eliminate some false positives
     printhead "--> usage of *0"
-    grep $_grepopts "[a-zA-Z0-9)]\+[ 	]*\*[ 	]*0[^.0-9xa-fA-F_]" $chfilelist
+    grep $_grepopts "[a-zA-Z0-9)]\+[ $TAB]*\*[ $TAB]*0[^.0-9xa-fA-F_]" $chfilelist
 
     printhead "--> usage of *1"
-    grep $_grepopts "[a-zA-Z0-9)]\+[ 	]*\*[ 	]*1[^.0-9ea-fA-F_]" $chfilelist
+    grep $_grepopts "[a-zA-Z0-9)]\+[ $TAB]*\*[ $TAB]*1[^.0-9ea-fA-F_]" $chfilelist
 
     printhead "--> usage of +0"
-    grep $_grepopts "[a-zA-Z0-9)]\+[ 	]*+[ 	]*0[^.0-9xa-fA-F_]" $chfilelist
+    grep $_grepopts "[a-zA-Z0-9)]\+[ $TAB]*+[ $TAB]*0[^.0-9xa-fA-F_]" $chfilelist
 
     printhead "--> usage of -0"
-    grep $_grepopts "[a-zA-Z0-9)]\+[ 	]*-[ 	]*0[^.0-9xa-fA-F_]" $chfilelist
+    grep $_grepopts "[a-zA-Z0-9)]\+[ $TAB]*-[ $TAB]*0[^.0-9xa-fA-F_]" $chfilelist
 fi
 
 # -----------------------------------------------------------------------------