diff --git a/README.md b/README.md
index cd9adaf..61f2cba 100644
--- a/README.md
+++ b/README.md
@@ -21,3 +21,5 @@ Impotent is still work-in-progress:
 Impotent requires C11 and an architecture with 8-byte atomic operations, but otherwise it is completely cross-platform.
 
 Performance-wise, it's surprisingly competitive with PoC Lua, considering how quickly it was made up to the point of writing this README (~2 weeks). By far the worst bottleneck is the GC, since it requires all threads and their heaps to synchronize.
+
+Certain Lua idioms become impossible under Impotent. For example the idiom of appending to tables (`t[#t + 1] = x`) isn't atomic, therefore `table.insert` should be used instead.
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