diff --git a/teavm-core/src/main/resources/org/teavm/javascript/runtime.js b/teavm-core/src/main/resources/org/teavm/javascript/runtime.js
index 9571d489f..9b7a826b8 100644
--- a/teavm-core/src/main/resources/org/teavm/javascript/runtime.js
+++ b/teavm-core/src/main/resources/org/teavm/javascript/runtime.js
@@ -21,7 +21,7 @@ $rt_compare = function(a, b) {
     return a > b ? 1 : a < b ? -1 : 0;
 }
 $rt_isInstance = function(obj, cls) {
-    return obj != null && obj.constructor.$meta && $rt_isAssignable(obj.constructor, cls);
+    return obj !== null && !!obj.constructor.$meta && $rt_isAssignable(obj.constructor, cls);
 }
 $rt_isAssignable = function(from, to) {
     if (from === to) {
diff --git a/teavm-html4j/src/main/java/org/teavm/html4j/JavaScriptConvGenerator.java b/teavm-html4j/src/main/java/org/teavm/html4j/JavaScriptConvGenerator.java
index 1ef4defb6..e68d243ed 100644
--- a/teavm-html4j/src/main/java/org/teavm/html4j/JavaScriptConvGenerator.java
+++ b/teavm-html4j/src/main/java/org/teavm/html4j/JavaScriptConvGenerator.java
@@ -116,8 +116,12 @@ public class JavaScriptConvGenerator implements Generator {
         writer.outdent().append("} else if (" + type + " === ").appendClass("java.lang.Double")
                 .append(") {").indent().softNewLine();
         writer.append("return ").appendMethodBody(valueOfDoubleMethod).append("(" + obj + ");").softNewLine();
-        writer.outdent().append("} else if (" + type + " === $rt_intcls()) {").indent().softNewLine();
+        writer.outdent().append("} else if (" + type + " === $rt_intcls() || " + type + " === $rt_bytecls() || " +
+                type + " === $rt_shortcls()) {").indent().softNewLine();
         writer.append("return " + obj + "|0;").softNewLine();
+        writer.outdent().append("} else if (" + type + " === $rt_doublecls() || " + type + " == $rt_floatcls()) {")
+                .indent().softNewLine();
+        writer.append("return " + obj + ";").softNewLine();
         writer.outdent().append("} else if (" + type + " === ").appendClass("java.lang.Boolean")
                 .append(") {").indent().softNewLine();
         writer.append("return ").appendMethodBody(valueOfBooleanMethod).append("(" + obj + "?1:0);").softNewLine();