diff --git a/builtin/grep.c b/builtin/grep.c
index 891e5eab3d..10a1f65310 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -414,10 +414,10 @@ static void *load_file(const char *filename, size_t *sz)
 	err_ret:
 		if (errno != ENOENT)
 			error(_("'%s': %s"), filename, strerror(errno));
-		return 0;
+		return NULL;
 	}
 	if (!S_ISREG(st.st_mode))
-		return 0;
+		return NULL;
 	*sz = xsize_t(st.st_size);
 	i = open(filename, O_RDONLY);
 	if (i < 0)
@@ -427,7 +427,7 @@ static void *load_file(const char *filename, size_t *sz)
 		error(_("'%s': short read %s"), filename, strerror(errno));
 		close(i);
 		free(data);
-		return 0;
+		return NULL;
 	}
 	close(i);
 	data[*sz] = 0;
diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index 5a67c8181e..31f001f105 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -294,7 +294,7 @@ static void *unpack_raw_entry(struct object_entry *obj, union delta_base *delta_
 	void *data;
 
 	obj->idx.offset = consumed_bytes;
-	input_crc32 = crc32(0, Z_NULL, 0);
+	input_crc32 = crc32(0, NULL, 0);
 
 	p = fill(1);
 	c = *p;
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 27050e7c16..e1ba4dc697 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -1,4 +1,4 @@
-#include "cache.h"
+#include "builtin.h"
 #include "pack.h"
 #include "refs.h"
 #include "pkt-line.h"
diff --git a/csum-file.c b/csum-file.c
index 4d50cc5ce1..be49d5fcf9 100644
--- a/csum-file.c
+++ b/csum-file.c
@@ -116,7 +116,7 @@ struct sha1file *sha1fd_throughput(int fd, const char *name, struct progress *tp
 
 void crc32_begin(struct sha1file *f)
 {
-	f->crc32 = crc32(0, Z_NULL, 0);
+	f->crc32 = crc32(0, NULL, 0);
 	f->do_crc = 1;
 }
 
diff --git a/pack-check.c b/pack-check.c
index c3bf21dbcb..a1a521648d 100644
--- a/pack-check.c
+++ b/pack-check.c
@@ -23,7 +23,7 @@ int check_pack_crc(struct packed_git *p, struct pack_window **w_curs,
 		   off_t offset, off_t len, unsigned int nr)
 {
 	const uint32_t *index_crc;
-	uint32_t data_crc = crc32(0, Z_NULL, 0);
+	uint32_t data_crc = crc32(0, NULL, 0);
 
 	do {
 		unsigned int avail;
diff --git a/pkt-line.c b/pkt-line.c
index cd1bd26413..5a04984ea3 100644
--- a/pkt-line.c
+++ b/pkt-line.c
@@ -1,7 +1,7 @@
 #include "cache.h"
 #include "pkt-line.h"
 
-const char *packet_trace_prefix = "git";
+static const char *packet_trace_prefix = "git";
 static const char trace_key[] = "GIT_TRACE_PACKET";
 
 void packet_trace_identity(const char *prog)
diff --git a/rerere.c b/rerere.c
index 3d00a71ff9..22dfc843da 100644
--- a/rerere.c
+++ b/rerere.c
@@ -438,7 +438,7 @@ static int merge(const char *name, const char *path)
 		ret = 1;
 		goto out;
 	}
-	ret = ll_merge(&result, path, &base, NULL, &cur, "", &other, "", 0);
+	ret = ll_merge(&result, path, &base, NULL, &cur, "", &other, "", NULL);
 	if (!ret) {
 		FILE *f;