diff --git a/include/extern.h b/include/extern.h
index 0761d224e..5812366f2 100644
--- a/include/extern.h
+++ b/include/extern.h
@@ -1932,6 +1932,7 @@ E void VDECL(verbalize, (const char *, ...)) PRINTF_F(1, 2);
 E void VDECL(raw_printf, (const char *, ...)) PRINTF_F(1, 2);
 E void VDECL(impossible, (const char *, ...)) PRINTF_F(1, 2);
 E void VDECL(config_error_add, (const char *, ...)) PRINTF_F(1, 2);
+E void FDECL(nhassert_failed, (const char *, const char *, int));
 
 /* ### polyself.c ### */
 
diff --git a/include/global.h b/include/global.h
index 6e0f96ebf..ada34523c 100644
--- a/include/global.h
+++ b/include/global.h
@@ -375,5 +375,10 @@ struct savefile_info {
 #define nethack_enter(argc, argv) ((void) 0)
 #endif
 
+/* Supply nhassert macro if not supplied by port */
+#ifndef nhassert
+#define nhassert(expression) (void)((!!(expression)) || \
+        (nhassert_failed(#expression, __FILE__, __LINE__), 0))
+#endif
 
 #endif /* GLOBAL_H */
diff --git a/include/ntconf.h b/include/ntconf.h
index 9d79006f0..62c269bab 100644
--- a/include/ntconf.h
+++ b/include/ntconf.h
@@ -267,16 +267,6 @@ extern int FDECL(set_win32_option, (const char *, const char *));
 extern int FDECL(alternative_palette, (char *));
 #endif
 
-#ifdef NDEBUG
-#define nhassert(expression) ((void)0)
-#else
-extern void FDECL(nhassert_failed, (const char * exp, const char * file,
-                                    int line));
-
-#define nhassert(expression) (void)((!!(expression)) || \
-        (nhassert_failed(#expression, __FILE__, __LINE__), 0))
-#endif
-
 #define nethack_enter(argc, argv) nethack_enter_winnt()
 extern void FDECL(nethack_exit, (int)) NORETURN;
 extern boolean FDECL(file_exists, (const char *));
diff --git a/src/pline.c b/src/pline.c
index d7db3f43d..535b75e95 100644
--- a/src/pline.c
+++ b/src/pline.c
@@ -582,4 +582,10 @@ VA_DECL(const char *, str)
 #endif
 }
 
+/* nhassert_failed is called when an nhassert's condition is false */
+void nhassert_failed(const char * exp, const char * file, int line)
+{
+    impossible("NHASSERT(%s) in '%s' at line %d", exp, file, line);
+}
+
 /*pline.c*/
diff --git a/sys/winnt/winnt.c b/sys/winnt/winnt.c
index d54982975..0e19e1f76 100644
--- a/sys/winnt/winnt.c
+++ b/sys/winnt/winnt.c
@@ -475,16 +475,6 @@ char *buf;
 }
 #endif /* RUNTIME_PORT_ID */
 
-/* nhassert_failed is called when an nhassert's condition is false */
-void nhassert_failed(const char * exp, const char * file, int line)
-{
-    char message[BUFSZ];
-    snprintf(message, sizeof(message),
-                "NHASSERT(%s) in '%s' at line %d", exp, file, line);
-
-    impossible(message);
-}
-
 void
 nethack_exit(code)
 int code;
diff --git a/win/tty/topl.c b/win/tty/topl.c
index 14e9bc548..bb79be26c 100644
--- a/win/tty/topl.c
+++ b/win/tty/topl.c
@@ -259,7 +259,7 @@ register const char *bp;
         && cw->cury == 0
         && n0 + (int) strlen(toplines) + 3 < CO - 8 /* room for --More-- */
         && (notdied = strncmp(bp, "You die", 7)) != 0) {
-        /* nhassert(strlen(toplines) == cw->curx); */
+        nhassert(strlen(toplines) == cw->curx);
         Strcat(toplines, "  ");
         Strcat(toplines, bp);
         cw->curx += 2;
@@ -313,7 +313,7 @@ char c;
         if (ttyDisplay->curx == 0 && ttyDisplay->cury > 0)
             tty_curs(BASE_WINDOW, CO, (int) ttyDisplay->cury - 1);
         backsp();
-        /* nhassert(ttyDisplay->curx > 0); */
+        nhassert(ttyDisplay->curx > 0);
         ttyDisplay->curx--;
         cw->curx = ttyDisplay->curx;
         return;
@@ -708,8 +708,8 @@ boolean restoring_msghist;
         dumplogmsg(toplines);
 #endif
     } else if (snapshot_mesgs) {
-        /* nhassert(ttyDisplay == NULL ||
-                 ttyDisplay->toplin != TOPLINE_NEED_MORE); */
+        nhassert(ttyDisplay == NULL ||
+                 ttyDisplay->toplin != TOPLINE_NEED_MORE);
 
         /* done putting arbitrary messages in; put the snapshot ones back */
         for (idx = 0; snapshot_mesgs[idx]; ++idx) {
diff --git a/win/tty/wintty.c b/win/tty/wintty.c
index 8ea315ab1..0422129fd 100644
--- a/win/tty/wintty.c
+++ b/win/tty/wintty.c
@@ -2321,7 +2321,7 @@ boolean blocking; /* with ttys, all windows are blocking */
             more();
             ttyDisplay->toplin = TOPLINE_NEED_MORE; /* more resets this */
             tty_clear_nhwindow(window);
-            /* nhassert(ttyDisplay->toplin == TOPLINE_EMPTY); */
+            nhassert(ttyDisplay->toplin == TOPLINE_EMPTY);
         } else
             ttyDisplay->toplin = TOPLINE_EMPTY;
         cw->curx = cw->cury = 0;
@@ -2409,7 +2409,7 @@ winid window;
     case NHW_MESSAGE:
         if (ttyDisplay->toplin != TOPLINE_EMPTY)
             tty_display_nhwindow(WIN_MESSAGE, TRUE);
-        /* nhassert(ttyDisplay->toplin == TOPLINE_EMPTY); */
+        nhassert(ttyDisplay->toplin == TOPLINE_EMPTY);
         /*FALLTHRU*/
     case NHW_STATUS:
     case NHW_BASE:
@@ -3164,7 +3164,7 @@ const char *mesg;
         more();
         ttyDisplay->toplin = TOPLINE_NEED_MORE; /* more resets this */
         tty_clear_nhwindow(WIN_MESSAGE);
-        /* nhassert(ttyDisplay->toplin == TOPLINE_EMPTY); */
+        nhassert(ttyDisplay->toplin == TOPLINE_EMPTY);
     }
     /* normally <ESC> means skip further messages, but in this case
        it means cancel the current prompt; any other messages should