diff --git a/src/apps/mellanox/connectx4.lua b/src/apps/mellanox/connectx4.lua
index ec21bb75b3..24a09b0dd7 100644
--- a/src/apps/mellanox/connectx4.lua
+++ b/src/apps/mellanox/connectx4.lua
@@ -163,8 +163,12 @@ local DEAD = 3
 -- Returns true on successful transition, false if oldstate does not match.
 function transition (cxq, oldstate, newstate)
    -- XXX use atomic x86 "LOCK CMPXCHG" instruction. Have to teach DynASM.
-   cxq.state = newstate
-   return true
+   if cxq.state == oldstate then
+      cxq.state = newstate
+      return true
+   else
+      return false
+   end
 end
 
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