diff --git a/extensions/python/xpcom/src/PyGInputStream.cpp b/extensions/python/xpcom/src/PyGInputStream.cpp
index 822dc580ee4..078e2f6512c 100644
--- a/extensions/python/xpcom/src/PyGInputStream.cpp
+++ b/extensions/python/xpcom/src/PyGInputStream.cpp
@@ -103,18 +103,23 @@ PyG_nsIInputStream::Read(char * buf, PRUint32 count, PRUint32 *_retval)
 	const char *methodName = "read";
 	nsresult nr = InvokeNativeViaPolicy(methodName, &ret, "i", count);
 	if (NS_SUCCEEDED(nr)) {
-		PRUint32 py_size;
+		Py_ssize_t py_size;
 		const void *py_buf;
-		if (PyObject_AsReadBuffer(ret, &py_buf, (int *)&py_size)!=0) {
+		if (PyObject_AsReadBuffer(ret, &py_buf, &py_size)!=0) {
 			PyErr_Format(PyExc_TypeError, "nsIInputStream::read() method must return a buffer object - not a '%s' object", ret->ob_type->tp_name);
 			nr = HandleNativeGatewayError(methodName);
 		} else {
-			if (py_size > count) {
-				PyXPCOM_LogWarning("nsIInputStream::read() was asked for %d bytes, but the string returned is %d bytes - truncating!\n", count, py_size);
-				py_size = count;
+		        if ( (py_size & 0xFFFFFFFF) != py_size) {
+		                PyErr_SetString(PyExc_RuntimeError, "Python Buffer length overflows 32-bit in PyObject_AsWriteBuffer");
+				nr = HandleNativeGatewayError(methodName);
+		        } else {
+				if (py_size > count) {
+					PyXPCOM_LogWarning("nsIInputStream::read() was asked for %d bytes, but the string returned is %d bytes - truncating!\n", count, py_size);
+					py_size = count;
+				}
+				memcpy(buf, py_buf, py_size);
+				*_retval = py_size;
 			}
-			memcpy(buf, py_buf, py_size);
-			*_retval = py_size;
 		}
 	}
 	return nr;
diff --git a/extensions/python/xpcom/src/PyIInputStream.cpp b/extensions/python/xpcom/src/PyIInputStream.cpp
index 67bdc549807..8e90b6b71e7 100644
--- a/extensions/python/xpcom/src/PyIInputStream.cpp
+++ b/extensions/python/xpcom/src/PyIInputStream.cpp
@@ -65,12 +65,19 @@ static PyObject *DoPyRead_Buffer(nsIInputStream *pI, PyObject *obBuffer, PRUint3
 {
 	PRUint32 nread;
 	void *buf;
-	PRUint32 buf_len;
-	if (PyObject_AsWriteBuffer(obBuffer, &buf, (int *)&buf_len) != 0) {
+	Py_ssize_t buf_len;
+	if (PyObject_AsWriteBuffer(obBuffer, &buf, &buf_len) != 0) {
 		PyErr_Clear();
 		PyErr_SetString(PyExc_TypeError, "The buffer object does not have a write buffer!");
 		return NULL;
 	}
+
+	if ( (buf_len & 0xFFFFFFFF) != buf_len) {
+		PyErr_Clear();
+		PyErr_SetString(PyExc_RuntimeError, "Python Buffer length overflows 32-bit in PyObject_AsWriteBuffer");
+		return NULL;
+	}
+
 	if (n==(PRUint32)-1) {
 		n = buf_len;
 	} else {
@@ -116,11 +123,17 @@ static PyObject *DoPyRead_Size(nsIInputStream *pI, PRUint32 n)
 		rc = PyBuffer_New(nread);
 		if (rc != NULL) {
 			void *ob_buf;
-			PRUint32 buf_len;
-			if (PyObject_AsWriteBuffer(rc, &ob_buf, (int *)&buf_len) != 0) {
+			Py_ssize_t buf_len;
+			if (PyObject_AsWriteBuffer(rc, &ob_buf, &buf_len) != 0) {
 				// should never fail - we just created it!
 				return NULL;
 			}
+
+			if ( (buf_len & 0xFFFFFFFF) != buf_len) {
+				PyErr_SetString(PyExc_RuntimeError, "Python Buffer length overflows 32-bit in PyObject_AsWriteBuffer");
+				return NULL;
+			}
+
 			if (buf_len != nread) {
 				PyErr_SetString(PyExc_RuntimeError, "New buffer isn't the size we created it!");
 				return NULL;
diff --git a/extensions/python/xpcom/src/PyXPCOM.h b/extensions/python/xpcom/src/PyXPCOM.h
index e5cc3be18de..1a879dd383c 100644
--- a/extensions/python/xpcom/src/PyXPCOM.h
+++ b/extensions/python/xpcom/src/PyXPCOM.h
@@ -78,6 +78,12 @@
 
 #include <Python.h>
 
+// python 2.4 doesn't have Py_ssize_t
+// => fallback to int
+#if PY_VERSION_HEX < 0x02050000 && !defined(PY_SSIZE_T_MIN)
+typedef int Py_ssize_t;
+#endif
+
 // PYXPCOM_EXPORT means 'exported from the pyxpcom core lib' - which changes
 // spelling depending on whether pyxpcom is being built or just referenced.
 #ifdef BUILD_PYXPCOM