diff --git a/cmd/rekor-cli/app/log_proof.go b/cmd/rekor-cli/app/log_proof.go
index c041abafb4e5b96f2428ba29a4751ae6e1feb6ba..05dc43184b95b3e2b6e003111b162c8b85da5b8a 100644
--- a/cmd/rekor-cli/app/log_proof.go
+++ b/cmd/rekor-cli/app/log_proof.go
@@ -55,15 +55,18 @@ var logProofCmd = &cobra.Command{
 		if err := viper.BindPFlags(cmd.Flags()); err != nil {
 			return fmt.Errorf("Error initializing cmd line args: %s", err)
 		}
-		if viper.GetUint64("first-size") > viper.GetUint64("last-size") {
-			return errors.New("last-size must be >= to first-size")
-		}
 		if viper.GetUint64("first-size") == 0 {
 			return errors.New("first-size must be > 0")
 		}
+		if !viper.IsSet("last-size") {
+			return errors.New("last-size must be specified")
+		}
 		if viper.GetUint64("last-size") == 0 {
 			return errors.New("last-size must be > 0")
 		}
+		if viper.GetUint64("first-size") > viper.GetUint64("last-size") {
+			return errors.New("last-size must be >= to first-size")
+		}
 		return nil
 	},
 	Run: format.WrapCmd(func(args []string) (interface{}, error) {