diff --git a/classlib/src/main/java/org/teavm/classlib/java/lang/TString.java b/classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
index fe0b43238..c9a49284c 100644
--- a/classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
+++ b/classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
@@ -413,8 +413,9 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
     }
 
     public boolean contains(TCharSequence s) {
+        int sz = length() - s.length();
         outer:
-        for (int i = 0; i < length(); ++i) {
+        for (int i = 0; i < sz; ++i) {
             for (int j = 0; j < s.length(); ++j) {
                 if (charAt(i + j) != s.charAt(j)) {
                     continue outer;
diff --git a/jso/impl/src/main/java/org/teavm/jso/impl/JSValueMarshaller.java b/jso/impl/src/main/java/org/teavm/jso/impl/JSValueMarshaller.java
index 59ce8caaa..eba3eb5f5 100644
--- a/jso/impl/src/main/java/org/teavm/jso/impl/JSValueMarshaller.java
+++ b/jso/impl/src/main/java/org/teavm/jso/impl/JSValueMarshaller.java
@@ -58,7 +58,7 @@ class JSValueMarshaller {
         if (type instanceof ValueType.Object) {
             String className = ((ValueType.Object) type).getClassName();
             ClassReader cls = classSource.get(className);
-            if (cls.getAnnotations().get(JSFunctor.class.getName()) != null) {
+            if (cls != null && cls.getAnnotations().get(JSFunctor.class.getName()) != null) {
                 return wrapFunctor(location, var, cls);
             }
         }
@@ -221,7 +221,7 @@ class JSValueMarshaller {
         if (type instanceof ValueType.Object) {
             String className = ((ValueType.Object) type).getClassName();
             ClassReader cls = classSource.get(className);
-            if (cls.getAnnotations().get(JSFunctor.class.getName()) != null) {
+            if (cls != null && cls.getAnnotations().get(JSFunctor.class.getName()) != null) {
                 return unwrapFunctor(location, var, cls);
             }
         }