diff --git a/context.go b/context.go
index ea4f8a325..17488e403 100644
--- a/context.go
+++ b/context.go
@@ -138,8 +138,8 @@ func (ctx Context) LoadModule(name string, rawMsg json.RawMessage) (interface{},
 				if err2 != nil {
 					err = fmt.Errorf("%v; additionally, cleanup: %v", err, err2)
 				}
-				return nil, fmt.Errorf("%s: invalid configuration: %v", mod.Name, err)
 			}
+			return nil, fmt.Errorf("%s: invalid configuration: %v", mod.Name, err)
 		}
 	}
 
diff --git a/modules/caddyhttp/caddyhttp.go b/modules/caddyhttp/caddyhttp.go
index 7d30178e9..3277e4298 100644
--- a/modules/caddyhttp/caddyhttp.go
+++ b/modules/caddyhttp/caddyhttp.go
@@ -102,7 +102,7 @@ func (app *App) Validate() error {
 			}
 			for _, a := range expanded {
 				if sn, ok := lnAddrs[netw+a]; ok {
-					return fmt.Errorf("listener address repeated: %s (already claimed by server '%s')", a, sn)
+					return fmt.Errorf("server %s: listener address repeated: %s (already claimed by server '%s')", srvName, a, sn)
 				}
 				lnAddrs[netw+a] = srvName
 			}
@@ -486,5 +486,9 @@ const (
 	DefaultHTTPSPort = 443
 )
 
-// Interface guard
-var _ caddy.App = (*App)(nil)
+// Interface guards
+var (
+	_ caddy.App         = (*App)(nil)
+	_ caddy.Provisioner = (*App)(nil)
+	_ caddy.Validator   = (*App)(nil)
+)
diff --git a/modules/caddyhttp/fileserver/staticfiles.go b/modules/caddyhttp/fileserver/staticfiles.go
index 67a337b11..0bb910d85 100644
--- a/modules/caddyhttp/fileserver/staticfiles.go
+++ b/modules/caddyhttp/fileserver/staticfiles.go
@@ -450,5 +450,9 @@ var defaultIndexNames = []string{"index.html"}
 
 const minBackoff, maxBackoff = 2, 5
 
-// Interface guard
-var _ caddyhttp.Handler = (*FileServer)(nil)
+// Interface guards
+var (
+	_ caddy.Provisioner = (*FileServer)(nil)
+	_ caddy.Validator   = (*FileServer)(nil)
+	_ caddyhttp.Handler = (*FileServer)(nil)
+)