diff --git a/README b/README
index d81ede9f..b70f75d5 100644
--- a/README
+++ b/README
@@ -63,6 +63,8 @@ Preparing system for tests (IRIX and Linux):
              - if TEST_LOGDEV and/or TEST_RTDEV, these will always be used.
              - if SCRATCH_LOGDEV and/or SCRATCH_RTDEV, the USE_EXTERNAL
                environment variable set to "yes" will enable their use.
+             - setenv DIFF_LENGTH "number of diff lines to print from a failed test",
+               by default 10, set to 0 to print the full diff
         - or add a case to the switch in common.config assigning
           these variables based on the hostname of your test
           machine
diff --git a/check b/check
index 75addb54..c20179c4 100755
--- a/check
+++ b/check
@@ -30,6 +30,8 @@ notrun=""
 interrupt=true
 
 export QA_CHECK_FS=${QA_CHECK_FS:=true}
+# number of diff lines from a failed test, 0 for whole output
+export DIFF_LENGTH=${DIFF_LENGTH:=10}
 
 # by default don't output timestamps
 timestamp=${TIMESTAMP:=false}
@@ -287,7 +289,12 @@ do
 		else
 		    echo " - output mismatch (see $seq.out.bad)"
 		    mv $tmp.out $seq.out.bad
-		    $diff $seq.out $seq.out.bad | head -n 10 | \
+		    $diff $seq.out $seq.out.bad | {
+		        if test "$DIFF_LENGTH" -le 0; then
+				cat
+			else
+				head -n "$DIFF_LENGTH"
+			fi; } | \
 			sed -e 's/^\(.\)/    \1/'
 		    echo "     ..."
 		    echo "     (Run '$diff $seq.out $seq.out.bad' to see the" \