diff --git a/tests/zfs-tests/include/math.shlib b/tests/zfs-tests/include/math.shlib
index 692a2a45b..7ac59f279 100644
--- a/tests/zfs-tests/include/math.shlib
+++ b/tests/zfs-tests/include/math.shlib
@@ -30,14 +30,15 @@ function within_percent
 	typeset percent=$3
 
 	# Set $a or $b to $2 such that a >= b
-	[[ '1' = $(echo "if ($2 > $a) 1" | bc) ]] && a=$2 || b=$2
+	[[ '1' = $(echo "if ($2 > $a) 1 else 0" | bc) ]] && a=$2 || b=$2
 
 	# Prevent division by 0
 	[[ $a =~ [1-9] ]] || return 1
 
 	typeset p=$(echo "scale=2; $b * 100 / $a" | bc)
 	log_note "Comparing $a and $b given $percent% (calculated: $p%)"
-	[[ '1' = $(echo "scale=2; if ($p >= $percent) 1" | bc) ]] && return 0
+	[[ '1' = $(echo "scale=2; if ($p >= $percent) 1 else 0" | bc) ]] && \
+	    return 0
 
 	return 1
 }