diff --git a/include/rapidjson/internal/strfunc.h b/include/rapidjson/internal/strfunc.h
index 2edfae5..de41d8f 100644
--- a/include/rapidjson/internal/strfunc.h
+++ b/include/rapidjson/internal/strfunc.h
@@ -28,6 +28,7 @@ namespace internal {
 */
 template <typename Ch>
 inline SizeType StrLen(const Ch* s) {
+    RAPIDJSON_ASSERT(s != 0);
     const Ch* p = s;
     while (*p) ++p;
     return SizeType(p - s);
@@ -36,6 +37,8 @@ inline SizeType StrLen(const Ch* s) {
 //! Returns number of code points in a encoded string.
 template<typename Encoding>
 bool CountStringCodePoint(const typename Encoding::Ch* s, SizeType length, SizeType* outCount) {
+    RAPIDJSON_ASSERT(s != 0);
+    RAPIDJSON_ASSERT(outCount != 0);
     GenericStringStream<Encoding> is(s);
     const typename Encoding::Ch* end = s + length;
     SizeType count = 0;
diff --git a/include/rapidjson/prettywriter.h b/include/rapidjson/prettywriter.h
index 0dcb0fe..c6f0216 100644
--- a/include/rapidjson/prettywriter.h
+++ b/include/rapidjson/prettywriter.h
@@ -91,12 +91,14 @@ public:
     bool Double(double d)       { PrettyPrefix(kNumberType); return Base::WriteDouble(d); }
 
     bool RawNumber(const Ch* str, SizeType length, bool copy = false) {
+        RAPIDJSON_ASSERT(str != 0);
         (void)copy;
         PrettyPrefix(kNumberType);
         return Base::WriteString(str, length);
     }
 
     bool String(const Ch* str, SizeType length, bool copy = false) {
+        RAPIDJSON_ASSERT(str != 0);
         (void)copy;
         PrettyPrefix(kStringType);
         return Base::WriteString(str, length);
@@ -184,7 +186,11 @@ public:
         \param type Type of the root of json.
         \note When using PrettyWriter::RawValue(), the result json may not be indented correctly.
     */
-    bool RawValue(const Ch* json, size_t length, Type type) { PrettyPrefix(type); return Base::WriteRawValue(json, length); }
+    bool RawValue(const Ch* json, size_t length, Type type) {
+        RAPIDJSON_ASSERT(json != 0);
+        PrettyPrefix(type);
+        return Base::WriteRawValue(json, length);
+    }
 
 protected:
     void PrettyPrefix(Type type) {
diff --git a/include/rapidjson/writer.h b/include/rapidjson/writer.h
index 94f22dd..c5a3b98 100644
--- a/include/rapidjson/writer.h
+++ b/include/rapidjson/writer.h
@@ -184,12 +184,14 @@ public:
     bool Double(double d)       { Prefix(kNumberType); return EndValue(WriteDouble(d)); }
 
     bool RawNumber(const Ch* str, SizeType length, bool copy = false) {
+        RAPIDJSON_ASSERT(str != 0);
         (void)copy;
         Prefix(kNumberType);
         return EndValue(WriteString(str, length));
     }
 
     bool String(const Ch* str, SizeType length, bool copy = false) {
+        RAPIDJSON_ASSERT(str != 0);
         (void)copy;
         Prefix(kStringType);
         return EndValue(WriteString(str, length));
@@ -249,7 +251,11 @@ public:
         \param length Length of the json.
         \param type Type of the root of json.
     */
-    bool RawValue(const Ch* json, size_t length, Type type) { Prefix(type); return EndValue(WriteRawValue(json, length)); }
+    bool RawValue(const Ch* json, size_t length, Type type) {
+        RAPIDJSON_ASSERT(json != 0);
+        Prefix(type);
+        return EndValue(WriteRawValue(json, length));
+    }
 
 protected:
     //! Information for each nested level