diff --git a/sh/minutemaid b/sh/minutemaid
index 76d7057..535e009 100755
--- a/sh/minutemaid
+++ b/sh/minutemaid
@@ -37,7 +37,7 @@ minutemaid() { ### @-
         o)  offset="$OPTARG";;
         ?)  local fd=0
             [ $name = h ] && fd=1 || fd=2
-            printf "%s\n" "usage: $0 [-o offset] {interval} [{command} [{args...}]]" >&$fd
+            printf '%s\n' "usage: $0 [-o offset] {interval} [{command} [{args...}]]" >&$fd
             [ $name = h ] && return 0 || return 1;;
         esac
     done
@@ -46,8 +46,10 @@ minutemaid() { ### @-
     local interval="${1:?no interval specified}"
     shift
 
-    if [ "$interval" -le 0 ]; then
-        printf "%s\n" "$0: interval must be positive" >&2
+    if [ "$interval" -gt 0 ] 2>/dev/null; then
+        :
+    else
+        printf "%s\n" "$0: interval must be a positive integer" >&2
         return 1
     fi