diff --git a/usr.bin/gprof/aout.c b/usr.bin/gprof/aout.c
index 76ad07ea86df..7907d466df68 100644
--- a/usr.bin/gprof/aout.c
+++ b/usr.bin/gprof/aout.c
@@ -132,7 +132,7 @@ getsymtab(FILE *nfile, const char *filename)
 	errx( 1 , "%s: no symbols" , filename );
     askfor = nname + 1;
     nl = (nltype *) calloc( askfor , sizeof(nltype) );
-    if (nl == 0)
+    if (nl == NULL)
 	errx( 1 , "no room for %zu bytes of symbol table" ,
 		askfor * sizeof(nltype) );
 
@@ -173,7 +173,7 @@ gettextspace(FILE *nfile)
 {
 
     textspace = (u_char *) malloc( xbuf.a_text );
-    if ( textspace == 0 ) {
+    if ( textspace == NULL ) {
 	warnx("no room for %u bytes of text space: can't do -c" ,
 		  xbuf.a_text );
 	return;
diff --git a/usr.bin/gprof/arcs.c b/usr.bin/gprof/arcs.c
index c5b2e96bbe06..4bea6c67186b 100644
--- a/usr.bin/gprof/arcs.c
+++ b/usr.bin/gprof/arcs.c
@@ -376,7 +376,7 @@ cyclelink(void)
 	 *	i.e. it is origin 1, not origin 0.
 	 */
     cyclenl = (nltype *) calloc( ncycle + 1 , sizeof( nltype ) );
-    if ( cyclenl == 0 )
+    if ( cyclenl == NULL )
 	errx( 1 , "no room for %zu bytes of cycle headers" ,
 		   ( ncycle + 1 ) * sizeof( nltype ) );
 	/*
@@ -479,7 +479,7 @@ cycleanalyze(void)
 	    continue;
 	done = FALSE;
         cyclestack = (arctype **) calloc( size + 1 , sizeof( arctype *) );
-	if ( cyclestack == 0 )
+	if ( cyclestack == NULL )
 	    errx( 1, "no room for %zu bytes of cycle stack" ,
 			   ( size + 1 ) * sizeof( arctype * ) );
 #	ifdef DEBUG
@@ -592,7 +592,7 @@ addcycle(arctype **stkstart, arctype **stkend)
     }
     clp = (cltype *)
 	calloc( 1 , sizeof ( cltype ) + ( size - 1 ) * sizeof( arctype * ) );
-    if ( clp == 0 ) {
+    if ( clp == NULL ) {
 	warnx( "no room for %zu bytes of subcycle storage" ,
 	    sizeof ( cltype ) + ( size - 1 ) * sizeof( arctype * ) );
 	return( FALSE );
diff --git a/usr.bin/gprof/gprof.c b/usr.bin/gprof/gprof.c
index e05d628e4cf8..879b0acb75ae 100644
--- a/usr.bin/gprof/gprof.c
+++ b/usr.bin/gprof/gprof.c
@@ -407,7 +407,7 @@ readsamples(FILE *pfile)
 
     if (samples == 0) {
 	samples = (double *) calloc(nsamples, sizeof(double));
-	if (samples == 0)
+	if (samples == NULL)
 	    errx(0, "no room for %d sample pc's", nsamples);
     }
     for (i = 0; i < nsamples; i++) {