diff --git a/src/lsp/mp.lsp b/src/lsp/mp.lsp
index b603a4cf1..e3dde9881 100644
--- a/src/lsp/mp.lsp
+++ b/src/lsp/mp.lsp
@@ -91,7 +91,7 @@ As interrupts are normally allowed WITH-INTERRUPTS only makes sense if there
 is an outer WITHOUT-INTERRUPTS with a corresponding ALLOW-WITH-INTERRUPTS:
 interrupts are not enabled if any outer WITHOUT-INTERRUPTS is not accompanied
 by ALLOW-WITH-INTERRUPTS."
-  (with-unique-names (allowp enablep)
+  (ext:with-unique-names (allowp enablep)
     ;; We could manage without ENABLEP here, but that would require
     ;; taking extra care not to ever have *ALLOW-WITH-INTERRUPTS* NIL
     ;; and *INTERRUPTS-ENABLED* T -- instead of risking future breakage