@@ -287,18 +287,7 @@ func (b *Builder) build(stdout io.Writer, stderr io.Writer, out io.Writer) (stri

 		}

 	}

-	// check if there are any leftover build-args that were passed but not

-	// consumed during build. Return a warning, if there are any.

-	leftoverArgs := []string{}

-	for arg := range b.options.BuildArgs {

-		if !b.isBuildArgAllowed(arg) {

-			leftoverArgs = append(leftoverArgs, arg)

-		}

-	}

-

-	if len(leftoverArgs) > 0 {

-		fmt.Fprintf(b.Stderr, "[Warning] One or more build-args %v were not consumed\n", leftoverArgs)

-	}

+	b.warnOnUnusedBuildArgs()

 	if b.image == "" {

 		return "", errors.New("No image was generated. Is your Dockerfile empty?")

@@ -326,6 +315,21 @@ func (b *Builder) build(stdout io.Writer, stderr io.Writer, out io.Writer) (stri

 	return b.image, nil

 }

+// check if there are any leftover build-args that were passed but not

+// consumed during build. Print a warning, if there are any.

+func (b *Builder) warnOnUnusedBuildArgs() {

+	leftoverArgs := []string{}

+	for arg := range b.options.BuildArgs {

+		if !b.isBuildArgAllowed(arg) {

+			leftoverArgs = append(leftoverArgs, arg)

+		}

+	}

+

+	if len(leftoverArgs) > 0 {

+		fmt.Fprintf(b.Stderr, "[Warning] One or more build-args %v were not consumed\n", leftoverArgs)

+	}

+}

+

 // Cancel cancels an ongoing Dockerfile build.

 func (b *Builder) Cancel() {

 	b.cancel()