diff --git a/mozilla/extensions/python/xpcom/src/PyIInputStream.cpp b/mozilla/extensions/python/xpcom/src/PyIInputStream.cpp
index a374b74470e..482550cee99 100644
--- a/mozilla/extensions/python/xpcom/src/PyIInputStream.cpp
+++ b/mozilla/extensions/python/xpcom/src/PyIInputStream.cpp
@@ -80,6 +80,9 @@ static PyObject *DoPyRead_Size(nsIInputStream *pI, PRUint32 n)
 		if (NS_FAILED(r))
 			return PyXPCOM_BuildPyException(r);
 	}
+	if (n==0) { // mozilla will assert if we alloc zero bytes.
+		return PyBuffer_New(0);
+	}
 	char *buf = (char *)nsMemory::Alloc(n);
 	if (buf==NULL) {
 		PyErr_NoMemory();
diff --git a/mozilla/extensions/python/xpcom/src/VariantUtils.cpp b/mozilla/extensions/python/xpcom/src/VariantUtils.cpp
index 20a4becf456..4454e8db37e 100644
--- a/mozilla/extensions/python/xpcom/src/VariantUtils.cpp
+++ b/mozilla/extensions/python/xpcom/src/VariantUtils.cpp
@@ -2482,6 +2482,7 @@ nsresult PyXPCOM_GatewayVariantHelper::BackFillVariant( PyObject *val, int index
 			if (val == Py_None)
 				break; // Remains NULL.
 			size_t nbytes = sequence_size * element_size;
+			if (nbytes==0) nbytes = 1; // avoid assertion about 0 bytes
 			*pp = (void *)nsMemory::Alloc(nbytes);
 			memset(*pp, 0, nbytes);
 			rc = FillSingleArray(*pp, val, sequence_size, element_size, array_type&XPT_TDP_TAGMASK);