diff --git a/test/test_cli.sh b/test/test_cli.sh
index 6aa2636b..1a593e9b 100755
--- a/test/test_cli.sh
+++ b/test/test_cli.sh
@@ -7,32 +7,6 @@
 
 . ./variables.sh
 
-# is a difference beyond a threshold? return 0 (meaning all ok) or 1 (meaning
-# error, or outside threshold)
-# 
-# use bc since bash does not support fp math
-break_threshold() {
-	diff=$1
-	threshold=$2
-	return $(echo "$diff <= $threshold" | bc -l)
-}
-
-# subtract, look for max difference less than a threshold
-test_difference() {
-	before=$1
-	after=$2
-	threshold=$3
-
-	$vips subtract $before $after $tmp/difference.v
-	$vips abs $tmp/difference.v $tmp/abs.v 
-	dif=$($vips max $tmp/abs.v)
-
-	if break_threshold $dif $threshold; then
-		echo "difference is $dif"
-		exit 1
-	fi
-}
-
 test_rotate() {
 	im=$1
 	inter=$2
diff --git a/test/test_connections.sh b/test/test_connections.sh
index de59c9a1..6fd13ed8 100755
--- a/test/test_connections.sh
+++ b/test/test_connections.sh
@@ -12,4 +12,6 @@ if test_supported jpegload_source; then
 
 	# test max difference < 10
 	test_difference $image $tmp/x.png 10
+else
+	exit 77
 fi
diff --git a/test/test_stall.sh b/test/test_stall.sh
index c1050c3c..3959a258 100755
--- a/test/test_stall.sh
+++ b/test/test_stall.sh
@@ -14,4 +14,6 @@ if test_supported tiffload; then
 -1 -1 -1
 EOF
 	VIPS_STALL=1 $vips conv $tmp/x.tif $tmp/x2.tif $tmp/mask.con
+else
+	exit 77
 fi
diff --git a/test/variables.sh.in b/test/variables.sh.in
index 6ea2dfd7..1af7b47c 100644
--- a/test/variables.sh.in
+++ b/test/variables.sh.in
@@ -32,9 +32,14 @@ test_supported() {
 
 # is a difference beyond a threshold? return 0 (meaning all ok) or 1 (meaning
 # error, or outside threshold)
+#
+# use bc since bash does not support fp math
 break_threshold() {
 	diff=$1
 	threshold=$2
+	if ! command -v bc >/dev/null; then
+		exit 77
+	fi
 	return $(echo "$diff <= $threshold" | bc -l)
 }