diff --git a/indra/llmessage/partsyspacket.cpp b/indra/llmessage/partsyspacket.cpp
index cfb3572d84bdfc50f0ee0fd468d4e1fecd3c1a0a..2f9e59accbe7f056665fc5e1859d76e54f90219a 100644
--- a/indra/llmessage/partsyspacket.cpp
+++ b/indra/llmessage/partsyspacket.cpp
@@ -144,6 +144,8 @@ LLPartSysCompressedPacket::LLPartSysCompressedPacket()
 		mData[i] = '\0';
 	}
 
+	mNumBytes = 0;
+
 	gSetInitDataDefaults(&mDefaults);
 }