diff --git a/src/mzscheme/src/env.c b/src/mzscheme/src/env.c
index 4a2507c9a8..723937a66f 100644
--- a/src/mzscheme/src/env.c
+++ b/src/mzscheme/src/env.c
@@ -2480,8 +2480,9 @@ scheme_lookup_binding(Scheme_Object *find_id, Scheme_Comp_Env *env, int flags,
 
 	if (!genv) {
 	  scheme_wrong_syntax("require", NULL, src_find_id, 
-			      "broken compiled code (phase %d, defn-phase %d): cannot find module %D",
-			      env->genv->phase, mod_defn_phase, modname);
+                              "namespace mismatch; reference (phase %d) to a module"
+                              " %D that is not instantiated (phase %d)", 
+			      env->genv->phase, modname, mod_defn_phase);
 	  return NULL;
 	}
       }
diff --git a/src/mzscheme/src/eval.c b/src/mzscheme/src/eval.c
index 42643beb3e..a12da7b427 100644
--- a/src/mzscheme/src/eval.c
+++ b/src/mzscheme/src/eval.c
@@ -1731,11 +1731,13 @@ static Scheme_Object *link_module_variable(Scheme_Object *modidx,
     
     if (!menv) {
       scheme_wrong_syntax("link", NULL, varname,
-			  "broken compiled code (phase %d, defn-phase %d, in %D), no declaration for module"
-			  ": %D", 
-			  env->phase, mod_phase,
-			  env->module ? env->module->modname : scheme_false,
-			  modname);
+			  "namespace mismatch; reference (phase %d) to a module"
+                          " %D that is not instantiated (phase %d); reference"
+			  " appears in module: %D", 
+			  env->phase,
+                          modname,
+                          mod_phase,
+                          env->module ? env->module->modname : scheme_false);
       return NULL;
     }
 
diff --git a/src/mzscheme/src/port.c b/src/mzscheme/src/port.c
index bb5f166ee5..e2c3a00b7b 100644
--- a/src/mzscheme/src/port.c
+++ b/src/mzscheme/src/port.c
@@ -771,7 +771,7 @@ void scheme_fdset(void *fd, int n)
 #endif
 #if defined(FILES_HAVE_FDS) || defined(USE_SOCKETS_TCP)
 # define STORED_ACTUAL_FDSET_LIMIT
-# define FDSET_LIMIT(fd) (*(int *)((char *)fd + dynamic_fd_size))
+# define FDSET_LIMIT(fd) (*(int *)((char *)fd XFORM_OK_PLUS dynamic_fd_size))
   int mx;
   mx = FDSET_LIMIT(fd);
   if (n > mx)