diff --git a/src/cmd/8c/cgen.c b/src/cmd/8c/cgen.c
index 8c5bf7b155d..1df03ef50c3 100644
--- a/src/cmd/8c/cgen.c
+++ b/src/cmd/8c/cgen.c
@@ -346,7 +346,7 @@ cgen(Node *n, Node *nn)
 				c = r->vconst;
 				if(c < 0)
 					c = -c;
-				v = log2(c);
+				v = xlog2(c);
 				if(v < 0)
 					break;
 				/* fall thru */
@@ -609,7 +609,7 @@ cgen(Node *n, Node *nn)
 				c = r->vconst;
 				if(c < 0)
 					c = -c;
-				v = log2(c);
+				v = xlog2(c);
 				if(v < 0)
 					break;
 				/* fall thru */