diff --git a/lib/alloca.c b/lib/alloca.c
index 836c5031..6ad425a4 100644
--- a/lib/alloca.c
+++ b/lib/alloca.c
@@ -169,7 +169,7 @@ static header *last_alloca_header = NULL;	/* -> last alloca header.  */
    implementations of C, for example under Gould's UTX/32.  */
 
 pointer
-alloca (unsigned size)
+alloca (size_t size)
 {
   auto char probe;		/* Probes stack depth: */
   register char *depth = ADDRESS_FUNCTION (probe);