diff --git a/gfx/graphite2/README.mozilla b/gfx/graphite2/README.mozilla
index 24c8861ee782..9d8def40f949 100644
--- a/gfx/graphite2/README.mozilla
+++ b/gfx/graphite2/README.mozilla
@@ -1,3 +1,6 @@
 This directory contains the Graphite2 library release 1.3.9 from
 https://github.com/silnrsi/graphite/releases/download/1.3.9/graphite2-minimal-1.3.9.tgz
 See gfx/graphite2/moz-gr-update.sh for update procedure.
+
+Cherry-picked post-1.3.9 commit 1ce331d5548b98ed8b818532b2556d6f2c7a3b83 to fix
+https://bugzilla.mozilla.org/show_bug.cgi?id=1345461.
diff --git a/gfx/graphite2/src/FeatureMap.cpp b/gfx/graphite2/src/FeatureMap.cpp
index b8c8405276a2..990616770d48 100644
--- a/gfx/graphite2/src/FeatureMap.cpp
+++ b/gfx/graphite2/src/FeatureMap.cpp
@@ -275,7 +275,7 @@ bool FeatureRef::applyValToFeature(uint32 val, Features & pDest) const
     else
       if (pDest.m_pMap!=&m_pFace->theSill().theFeatureMap())
         return false;       //incompatible
-    pDest.reserve(m_index);
+    pDest.reserve(m_index + 1);
     pDest[m_index] &= ~m_mask;
     pDest[m_index] |= (uint32(val) << m_bits);
     return true;