diff --git a/lib/libc/xdr/xdr.c b/lib/libc/xdr/xdr.c
index 59a843405ab..47aafea4bc3 100644
--- a/lib/libc/xdr/xdr.c
+++ b/lib/libc/xdr/xdr.c
@@ -696,6 +696,13 @@ xdr_string(XDR *xdrs, char **cpp, u_int maxsize)
 		if (sp == NULL) {
 			return(TRUE);	/* already free */
 		}
+		/*
+		 * XXX: buggy software may call this without a third
+		 * argument via xdr_free().  Ignore maxsize since it may
+		 * be invalid.  Otherwise, if it's very small, we might
+		 * fail to free the string.
+		 */
+		maxsize = RPC_MAXDATASIZE;
 		/* FALLTHROUGH */
 	case XDR_ENCODE:
 		size = strlen(sp);
diff --git a/sys/xdr/xdr.c b/sys/xdr/xdr.c
index 81d238ebf19..f983a474abd 100644
--- a/sys/xdr/xdr.c
+++ b/sys/xdr/xdr.c
@@ -620,6 +620,13 @@ xdr_string(XDR *xdrs, char **cpp, u_int maxsize)
 		if (sp == NULL) {
 			return(TRUE);	/* already free */
 		}
+		/*
+		 * XXX: buggy software may call this without a third
+		 * argument via xdr_free().  Ignore maxsize since it may
+		 * be invalid.  Otherwise, if it's very small, we might
+		 * fail to free the string.
+		 */
+		maxsize = RPC_MAXDATASIZE;
 		/* FALLTHROUGH */
 	case XDR_ENCODE:
 		size = strlen(sp);