diff --git a/libguile/posix.c b/libguile/posix.c
index 4564cb33b..4ca8d5ff7 100644
--- a/libguile/posix.c
+++ b/libguile/posix.c
@@ -2137,8 +2137,8 @@ SCM_DEFINE (scm_nice, "nice", 1, 0, 0,
   /* nice() returns "prio-NZERO" on success or -1 on error, but -1 can arise
      from "prio-NZERO", so an error must be detected from errno changed */
   errno = 0;
-  nice (scm_to_int (incr));
-  if (errno != 0)
+  int prio = nice (scm_to_int (incr));
+  if (prio == -1 && errno != 0)
     SCM_SYSERROR;
 
   return SCM_UNSPECIFIED;