diff --git a/lib/compress.js b/lib/compress.js
index 3847015dbe..384e0e89c8 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -3396,12 +3396,14 @@ merge(Compressor.prototype, {
                 if (prop instanceof AST_Node) break;
                 prop = "" + prop;
                 var diff = prop == "__proto__" || compressor.has_directive("use strict") ? function(node) {
-                    return typeof node.key == "string" && node.key != prop;
+                    var key = node.key;
+                    return typeof key == "string" && key != prop && key != "__proto__";
                 } : function(node) {
+                    var key = node.key;
                     if (node instanceof AST_ObjectGetter || node instanceof AST_ObjectSetter) {
-                        return typeof node.key == "string" && node.key != prop;
+                        return typeof key == "string" && key != prop;
                     }
-                    return true;
+                    return key !== "__proto__";
                 };
                 if (!all(value.properties, diff)) break;
                 value.properties.push(make_node(AST_ObjectKeyVal, node, {
@@ -5141,12 +5143,12 @@ merge(Compressor.prototype, {
             return true;
         }
         def(AST_Node, return_false);
-        def(AST_Array, function() {
-            return all_constant(this.elements);
+        def(AST_Array, function(scope) {
+            return all_constant(this.elements, scope);
         });
-        def(AST_Binary, function() {
-            return this.left.is_constant_expression()
-                && this.right.is_constant_expression()
+        def(AST_Binary, function(scope) {
+            return this.left.is_constant_expression(scope)
+                && this.right.is_constant_expression(scope)
                 && (this.operator != "in" || is_object(this.right));
         });
         def(AST_Class, function(scope) {
@@ -5198,14 +5200,14 @@ merge(Compressor.prototype, {
             }));
             return result;
         });
-        def(AST_Object, function() {
-            return all_constant(this.properties);
+        def(AST_Object, function(scope) {
+            return all_constant(this.properties, scope);
         });
-        def(AST_ObjectProperty, function() {
-            return typeof this.key == "string" && this.value.is_constant_expression();
+        def(AST_ObjectProperty, function(scope) {
+            return typeof this.key == "string" && this.value.is_constant_expression(scope);
         });
-        def(AST_Unary, function() {
-            return this.expression.is_constant_expression();
+        def(AST_Unary, function(scope) {
+            return this.expression.is_constant_expression(scope);
         });
     })(function(node, func) {
         node.DEFMETHOD("is_constant_expression", func);
diff --git a/test/compress/join_vars.js b/test/compress/join_vars.js
index 21b76aaa47..8925126663 100644
--- a/test/compress/join_vars.js
+++ b/test/compress/join_vars.js
@@ -1024,7 +1024,7 @@ issue_3856: {
     expect_stdout: "undefined"
 }
 
-issue_3916: {
+issue_3916_1: {
     options = {
         join_vars: true,
     }
@@ -1044,8 +1044,8 @@ issue_3916: {
         var o = {
             p: "PASS",
             __proto__: 42,
-            q: "FAIL",
         };
+        o.q = "FAIL";
         o.__proto__ = {
             p: "FAIL",
             q: "PASS",
@@ -1056,6 +1056,62 @@ issue_3916: {
     expect_stdout: "object PASS true PASS"
 }
 
+issue_3916_2: {
+    options = {
+        join_vars: true,
+    }
+    input: {
+        var log = console.log, o = {};
+        o.p = "FAIL 1";
+        o.__proto__ = {
+            get p() {
+                return "FAIL 2";
+            },
+            set p(u) {
+                log("FAIL 3");
+            },
+            set q(v) {
+                log("PASS 1");
+            },
+            get q() {
+                return "PASS 3";
+            },
+        };
+        o.p = "PASS 2";
+        o.q = "FAIL 4";
+        log(o.p);
+        log(o.q);
+    }
+    expect: {
+        var log = console.log, o = {
+            p: "FAIL 1",
+            __proto__: {
+                get p() {
+                    return "FAIL 2";
+                },
+                set p(u) {
+                    log("FAIL 3");
+                },
+                set q(v) {
+                    log("PASS 1");
+                },
+                get q() {
+                    return "PASS 3";
+                },
+            },
+        };
+        o.p = "PASS 2";
+        o.q = "FAIL 4";
+        log(o.p);
+        log(o.q);
+    }
+    expect_stdout: [
+        "PASS 1",
+        "PASS 2",
+        "PASS 3",
+    ]
+}
+
 assign_var: {
     options = {
         join_vars: true,
diff --git a/test/ufuzz/index.js b/test/ufuzz/index.js
index 8ccaefe0df..b48a418a1d 100644
--- a/test/ufuzz/index.js
+++ b/test/ufuzz/index.js
@@ -1188,7 +1188,7 @@ function createStatement(recurmax, canThrow, canBreak, canContinue, cannotReturn
 
 function createSwitchParts(recurmax, n, canThrow, canBreak, canContinue, cannotReturn, stmtDepth) {
     var hadDefault = false;
-    var s = [""];
+    var s = [ "" ];
     canBreak = enableLoopControl(canBreak, CAN_BREAK);
     while (n-- > 0) {
         //hadDefault = n > 0; // disables weird `default` clause positioning (use when handling destabilizes)
@@ -1619,6 +1619,10 @@ var KEYS = [
     "1.5",
     "3",
 ].concat(SAFE_KEYS);
+SAFE_KEYS = SAFE_KEYS.concat(SAFE_KEYS);
+SAFE_KEYS = SAFE_KEYS.concat(SAFE_KEYS);
+SAFE_KEYS = SAFE_KEYS.concat(SAFE_KEYS);
+SAFE_KEYS.push("__proto__");
 
 function getDotKey(assign) {
     var key;
@@ -1736,8 +1740,9 @@ function createObjectFunction(recurmax, stmtDepth, canThrow, internal, isClazz)
 
 function createObjectLiteral(recurmax, stmtDepth, canThrow) {
     recurmax--;
-    var obj = ["({"];
+    var obj = [ "({" ];
     var offset = SUPPORT.spread_object ? 0 : SUPPORT.computed_key ? 2 : 4;
+    var has_proto = false;
     for (var i = rng(6); --i >= 0;) switch (offset + rng(50 - offset)) {
       case 0:
         obj.push("..." + getVarName() + ",");
@@ -1753,7 +1758,12 @@ function createObjectLiteral(recurmax, stmtDepth, canThrow) {
         obj.push(createObjectFunction(recurmax, stmtDepth, canThrow) + ",");
         break;
       default:
-        obj.push(createObjectKey(recurmax, stmtDepth, canThrow) + ": " + createExpression(recurmax, COMMA_OK, stmtDepth, canThrow) + ",");
+        if (has_proto || rng(200)) {
+            obj.push(createObjectKey(recurmax, stmtDepth, canThrow) + ": " + createExpression(recurmax, COMMA_OK, stmtDepth, canThrow) + ",");
+        } else {
+            obj.push("__proto__: " + createExpression(recurmax, COMMA_OK, stmtDepth, canThrow) + " || {},");
+            has_proto = true;
+        }
         break;
     }
     obj.push("})");