diff --git a/Documentation/coccinelle.txt b/Documentation/coccinelle.txt
index 64daaf18874b..2516c5ef1691 100644
--- a/Documentation/coccinelle.txt
+++ b/Documentation/coccinelle.txt
@@ -157,6 +157,26 @@ semantic patch as shown in the previous section.
 The "report" mode is the default. You can select another one with the
 MODE variable explained above.
 
+ Debugging Coccinelle SmPL patches
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Using coccicheck is best as it provides in the spatch command line
+include options matching the options used when we compile the kernel.
+You can learn what these options are by using V=1, you could then
+manually run Coccinelle with debug options added.
+
+Alternatively you can debug running Coccinelle against SmPL patches
+by asking for stderr to be redirected to stderr, by default stderr
+is redirected to /dev/null, if you'd like to capture stderr you
+can specify the DEBUG_FILE="file.txt" option to coccicheck. For
+instance:
+
+    rm -f cocci.err
+    make coccicheck COCCI=scripts/coccinelle/free/kfree.cocci MODE=report DEBUG_FILE=cocci.err
+    cat cocci.err
+
+DEBUG_FILE support is only supported when using coccinelle >= 1.2.
+
  Additional flags
 ~~~~~~~~~~~~~~~~~~
 
diff --git a/scripts/coccicheck b/scripts/coccicheck
index 4b65a0fd50a1..3f0bb3f0fddc 100755
--- a/scripts/coccicheck
+++ b/scripts/coccicheck
@@ -96,7 +96,15 @@ run_cmd_parmap() {
 	if [ $VERBOSE -ne 0 ] ; then
 		echo "Running ($NPROC in parallel): $@"
 	fi
-	$@ 2>/dev/null
+	if [ "$DEBUG_FILE" != "/dev/null" -a "$DEBUG_FILE" != "" ]; then
+		if [ -f $DEBUG_FILE ]; then
+			echo "Debug file $DEBUG_FILE exists, bailing"
+			exit
+		fi
+	else
+		DEBUG_FILE="/dev/null"
+	fi
+	$@ 2>$DEBUG_FILE
 	if [[ $? -ne 0 ]]; then
 		echo "coccicheck failed"
 		exit $?