diff --git a/302stack_allocate.subx b/302stack_allocate.subx
index 4634039d..cd51d5ff 100644
--- a/302stack_allocate.subx
+++ b/302stack_allocate.subx
@@ -1,6 +1,6 @@
 # A function which pushes n zeros on the stack.
-# Not really useful to call manually.
-# The Mu compiler uses it when defining arrays on the stack.
+# Really only intended to be called from code generated by mu.subx (for array
+# vars on the stack).
 
 == code
 
diff --git a/308allocate-array.subx b/308allocate-array.subx
index c243ee33..5cc0fe1b 100644
--- a/308allocate-array.subx
+++ b/308allocate-array.subx
@@ -1,4 +1,5 @@
 # 2-arg version of allocate-array.
+# Really only intended to be called from code generated by mu.subx.
 
 == code
 
diff --git a/310copy-bytes.subx b/310copy-bytes.subx
index 176c4c33..2586a53f 100644
--- a/310copy-bytes.subx
+++ b/310copy-bytes.subx
@@ -1,4 +1,5 @@
-# Fill a region of memory with zeroes.
+# Some helpers for copying non-overlapping regions of memory.
+# Really only intended to be called from code generated by mu.subx.
 
 == code