diff --git a/cmd/build.go b/cmd/build.go
index 8e1986b5..a60231d7 100644
--- a/cmd/build.go
+++ b/cmd/build.go
@@ -84,7 +84,7 @@ kn func build --builder cnbs/sample-builder:bionic
 	return cmd
 }
 
-func ValidNamespaceAndRegistry() survey.Validator {
+func ValidNamespaceAndRegistry(path string) survey.Validator {
 	return func(val interface{}) error {
 
 		// if the value passed in is the zero value of the appropriate type
@@ -92,10 +92,10 @@ func ValidNamespaceAndRegistry() survey.Validator {
 			return errors.New("Value is required")
 		}
 
-		_, err := fn.DerivedImage("", val.(string)) //image can be derived without any error
+		_, err := fn.DerivedImage(path, val.(string)) //image can be derived without any error
 
 		if err != nil {
-			return errors.New(val.(string) + " Registry and Namespace are required (ie. docker.io/tigerteam). The image name will be derived from the function name.")
+			return fmt.Errorf("Invalid registry [%s] %v", val.(string), err)
 		}
 		return nil
 	}
@@ -120,6 +120,14 @@ func runBuild(cmd *cobra.Command, _ []string, clientFn buildClientFn) (err error
 		return fmt.Errorf("the given path '%v' does not contain an initialized function. Please create one at this path before deploying", config.Path)
 	}
 
+	// If a registry name was provided as a command line flag, it should be validated
+	if config.Registry != "" {
+		err = ValidNamespaceAndRegistry(config.Path)(config.Registry)
+		if err != nil {
+			return
+		}
+	}
+
 	// If the Function does not yet have an image name and one was not provided on the command line
 	if function.Image == "" {
 		//  AND a --registry was not provided, then we need to
@@ -129,7 +137,7 @@ func runBuild(cmd *cobra.Command, _ []string, clientFn buildClientFn) (err error
 
 			err = survey.AskOne(
 				&survey.Input{Message: "Registry for Function images:"},
-				&config.Registry, survey.WithValidator(ValidNamespaceAndRegistry()))
+				&config.Registry, survey.WithValidator(ValidNamespaceAndRegistry(config.Path)))
 			if err != nil {
 				if err == terminal.InterruptErr {
 					return nil
diff --git a/cmd/build_test.go b/cmd/build_test.go
new file mode 100644
index 00000000..199a46a2
--- /dev/null
+++ b/cmd/build_test.go
@@ -0,0 +1,51 @@
+package cmd
+
+import (
+	"io/ioutil"
+	"testing"
+
+	fn "knative.dev/kn-plugin-func"
+	"knative.dev/kn-plugin-func/mock"
+)
+
+// TestBuildInvalidRegistry ensures that running build specifying the name of the
+// registry explicitly as an argument invokes the registry validation code.
+func TestBuildInvalidRegistry(t *testing.T) {
+	var (
+		args    = []string{"--registry", "foo/bar/foobar/boofar"} // provide an invalid registry name
+		builder = mock.NewBuilder()                               // with a mock builder
+	)
+
+	// Run this test in a temporary directory
+	defer fromTempDir(t)()
+	// Write a func.yaml config which does not specify an image
+	funcYaml := `name: testymctestface
+namespace: ""
+runtime: go
+image: ""
+imageDigest: ""
+builder: quay.io/boson/faas-go-builder
+builders:
+  default: quay.io/boson/faas-go-builder
+envs: []
+annotations: {}
+labels: []
+created: 2021-01-01T00:00:00+00:00
+`
+	if err := ioutil.WriteFile("func.yaml", []byte(funcYaml), 0600); err != nil {
+		t.Fatal(err)
+	}
+
+	// Create a command with a client constructor fn that instantiates a client
+	// with a the mocked builder.
+	cmd := NewBuildCmd(func(_ buildConfig) (*fn.Client, error) {
+		return fn.New(fn.WithBuilder(builder)), nil
+	})
+
+	// Execute the command
+	cmd.SetArgs(args)
+	err := cmd.Execute()
+	if err == nil {
+		t.Fatal("Expected error")
+	}
+}