diff --git a/handler.go b/handler.go
index 93d9663..a25cdc6 100644
--- a/handler.go
+++ b/handler.go
@@ -6,14 +6,16 @@ import (
 	"time"
 )
 
-// Handler returns an http handler that requires a "seconds" query argument
-// and produces a profile over this duration. The optional "format" parameter
-// controls if the output is written in Google's "pprof" format (default) or
-// Brendan Gregg's "folded" stack format.
+// Handler returns an http handler that takes an optional "seconds" query
+// argument that defaults to "30" and produces a profile over this duration.
+// The optional "format" parameter controls if the output is written in
+// Google's "pprof" format (default) or Brendan Gregg's "folded" stack format.
 func Handler() http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		var seconds int
-		if _, err := fmt.Sscanf(r.URL.Query().Get("seconds"), "%d", &seconds); err != nil {
+		if s := r.URL.Query().Get("seconds"); s == "" {
+			seconds = 30
+		} else if _, err := fmt.Sscanf(s, "%d", &seconds); err != nil || seconds <= 0 {
 			w.WriteHeader(http.StatusBadRequest)
 			fmt.Fprintf(w, "bad seconds: %d: %s\n", seconds, err)
 		}