diff --git a/cli/README.md b/cli/README.md
index e7f189007..cfca67191 100644
--- a/cli/README.md
+++ b/cli/README.md
@@ -67,7 +67,7 @@ Translates between file formats and generates static code.
 
   --force-long     Enforces the use of 'Long' for s-/u-/int64 and s-/fixed64 fields.
   --force-number   Enforces the use of 'number' for s-/u-/int64 and s-/fixed64 fields.
-  --force-message  Enforces the use of message instances instead of plain objects.
+  --force-message  Enforces the use of message instances instead of plain objects for method calls.
 
 usage: pbjs [options] file1.proto file2.json ...  (or pipe)  other | pbjs [options] -
 ```
diff --git a/cli/pbjs.js b/cli/pbjs.js
index 150a2b6f0..fd0d84fd7 100644
--- a/cli/pbjs.js
+++ b/cli/pbjs.js
@@ -145,7 +145,7 @@ exports.main = function main(args, callback) {
                 "",
                 "  --force-long     Enforces the use of 'Long' for s-/u-/int64 and s-/fixed64 fields.",
                 "  --force-number   Enforces the use of 'number' for s-/u-/int64 and s-/fixed64 fields.",
-                "  --force-message  Enforces the use of message instances instead of plain objects.",
+                "  --force-message  Enforces the use of message instances instead of plain objects for method calls.",
                 "",
                 "  --null-defaults  Default value for optional fields is null instead of zero value.",
                 "",
diff --git a/cli/targets/static.js b/cli/targets/static.js
index c130d9026..4ec14b2d0 100644
--- a/cli/targets/static.js
+++ b/cli/targets/static.js
@@ -311,9 +311,13 @@ function buildFunction(type, functionName, gen, scope) {
         push("};");
 }
 
-function toJsType(field) {
+function toJsType(field, asInterface) {
     var type;
 
+    // Never declare enums as interfaces
+    if (field.resolvedType != null && field.resolvedType instanceof protobuf.Enum)
+        asInterface = false;
+
     switch (field.type) {
         case "double":
         case "float":
@@ -342,7 +346,7 @@ function toJsType(field) {
             break;
         default:
             if (field.resolve().resolvedType)
-                type = exportName(field.resolvedType, !(field.resolvedType instanceof protobuf.Enum || config.forceMessage));
+                type = exportName(field.resolvedType, asInterface);
             else
                 type = "*"; // should not happen
             break;
@@ -365,9 +369,9 @@ function buildType(ref, type) {
         type.fieldsArray.forEach(function(field) {
             var prop = util.safeProp(field.name); // either .name or ["name"]
             prop = prop.substring(1, prop.charAt(0) === "[" ? prop.length - 1 : prop.length);
-            var jsType = toJsType(field);
+            var jsType = toJsType(field, /*asInterface = */ true);
             if (field.optional)
-                jsType = jsType + "|null";
+                jsType = jsType + "|null|undefined";  // Incoming properties can include undefined members
             typeDef.push("@property {" + jsType + "} " + (field.optional ? "[" + prop + "]" : prop) + " " + (field.comment || type.name + " " + field.name));
         });
         push("");
@@ -393,9 +397,9 @@ function buildType(ref, type) {
         var prop = util.safeProp(field.name);
         if (config.comments) {
             push("");
-            var jsType = toJsType(field);
+            var jsType = toJsType(field, /*asInterface = */ false);
             if (field.optional && !field.map && !field.repeated && (field.resolvedType instanceof Type || config["null-defaults"]) || field.partOf)
-                jsType = jsType + "|null|undefined";
+                jsType = jsType + "|null";  // Members are never undefined, they are initialized in the prototype
             pushComment([
                 field.comment || type.name + " " + field.name + ".",
                 "@member {" + jsType + "} " + field.name,