diff --git a/modules/src/assert/BadAssert.c b/modules/src/assert/BadAssert.c
index 82c8222a2..c1cccb53d 100644
--- a/modules/src/assert/BadAssert.c
+++ b/modules/src/assert/BadAssert.c
@@ -24,6 +24,7 @@ wr_num(fd, n)
 	sys_write(fd, s, 1);
 }
 
+int
 _BadAssertion(file, lineno, assertion)
 	char *file, *assertion;
 	int lineno;
@@ -36,4 +37,5 @@ _BadAssertion(file, lineno, assertion)
 	sys_write(STDERR, assertion, strlen(assertion));
 	sys_write(STDERR, "\" failed\n", 9);
 	sys_stop(S_ABORT);
+	return 0;
 }
diff --git a/modules/src/assert/assert.3 b/modules/src/assert/assert.3
index d3da1cf3c..8f5f6ecb7 100644
--- a/modules/src/assert/assert.3
+++ b/modules/src/assert/assert.3
@@ -33,7 +33,7 @@ It causes a
 .IR sys_stop (S_ABORT)
 with a diagnostic comment on standard error.
 .PP
-The assertions are enabled by defining the preprocessor constant DEBUG.
+The assertions are disabled by defining the preprocessor constant NDEBUG.
 .SH DIAGNOSTICS
 .IR fn ,
 line
diff --git a/modules/src/assert/assert.h b/modules/src/assert/assert.h
index 50cbb98ec..f630add3e 100644
--- a/modules/src/assert/assert.h
+++ b/modules/src/assert/assert.h
@@ -5,13 +5,20 @@
 /* $Header$ */
 /*	 A S S E R T I O N    M A C R O   D E F I N I T I O N		*/
 
-#ifdef	DEBUG
-#ifdef __STDC__
-#define	assert(exp)	((exp) || _BadAssertion(__FILE__, __LINE__, #exp))
+/* This 'assert' definition can be used in a ,-expression. */
+
+#ifndef	NDEBUG
+#if __STDC__
+int _BadAssertion(char *, int, char *);
+#define	assert(exp)	((void)((exp) || _BadAssertion(__FILE__, __LINE__, #exp)))
 #else
 /*	Note: this macro uses parameter substitution inside strings */
 #define	assert(exp)	((exp) || _BadAssertion(__FILE__, __LINE__, "exp"))
 #endif
 #else
-#define	assert(exp)	(1)
-#endif	/* DEBUG */
+#if __STDC__
+#define	assert(exp)	((void)0)
+#else
+#define	assert(exp)	(0)
+#endif
+#endif	/* NDEBUG */