diff --git a/include/misc.h b/include/misc.h
index ca9b8a9d..e89a016f 100644
--- a/include/misc.h
+++ b/include/misc.h
@@ -123,6 +123,15 @@ typedef short coord;
 #define hours(x)	(60*60*(x))
 #define days(x)		(60*60*24*(x))
 
+extern int debug;
+
+/*
+ * If EXPR is true, an internal error occured.
+ * Return EXPR != 0.
+ * Usage: if (CANT_HAPPEN(...)) recovery_code();
+ */
+#define CANT_HAPPEN(expr) ((expr) ? oops(#expr, __FILE__, __LINE__) : 0)
+
 typedef int (*qsort_func_t) (const void *, const void *);
 
 	/* return codes from command routines */
diff --git a/include/prototypes.h b/include/prototypes.h
index 553940fe..59b25bc2 100644
--- a/include/prototypes.h
+++ b/include/prototypes.h
@@ -128,6 +128,7 @@ extern int has_helpful_engineer(coord x, coord y, natid cn);
 /* log.c */
 extern void loginit(s_char *);
 extern void logerror(s_char *, ...) ATTRIBUTE((format (printf, 1, 2)));
+extern int oops(char *, char *, int);
 /* maps.c */
 extern int draw_map(int, s_char, int, struct nstr_sect *, int);
 extern int unit_map(int, int, struct nstr_sect *, s_char *);
diff --git a/src/lib/common/log.c b/src/lib/common/log.c
index f3200ec7..4e959896 100644
--- a/src/lib/common/log.c
+++ b/src/lib/common/log.c
@@ -99,3 +99,15 @@ logerror(s_char *format, ...)
 #endif
     va_end(list);
 }
+
+/*
+ * Log internal error MSG occured in FILE:LINE.
+ * If debugging, call abort(), else return 1.
+ */
+int
+oops(char *msg, char *file, int line)
+{
+  logerror("Oops: %s in %s:%d\n", msg, file, line);
+  if (debug) abort();
+  return 1;
+}
diff --git a/src/server/main.c b/src/server/main.c
index 0af848f4..fbe69c52 100644
--- a/src/server/main.c
+++ b/src/server/main.c
@@ -80,13 +80,19 @@ static void loc_NTTerm(void);
 static int mainpid = 0;
 #endif
 
+/*
+ * Debugging?
+ * If yes, don't fork into background, don't catch certain signals,
+ * call abort() on internal error.
+ */
+int debug = 0;
+
 int
 main(int argc, char **argv)
 {
     time_t now;
     int hour[2];
     int flags = 0;
-    int debug = 0;
     int op;
     char *config_file = NULL;
     extern char *optarg;