diff --git a/builtin/get-tar-commit-id.c b/builtin/get-tar-commit-id.c
index e21c5416cd..6d9a79f9b3 100644
--- a/builtin/get-tar-commit-id.c
+++ b/builtin/get-tar-commit-id.c
@@ -33,8 +33,7 @@ int cmd_get_tar_commit_id(int argc, const char **argv, const char *prefix)
 	if (!skip_prefix(content, "52 comment=", &comment))
 		return 1;
 
-	n = write_in_full(1, comment, 41);
-	if (n < 41)
+	if (write_in_full(1, comment, 41) < 0)
 		die_errno("git get-tar-commit-id: write error");
 
 	return 0;
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 52c63ebfdc..dd06b3fb4f 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -743,7 +743,7 @@ static int run_and_feed_hook(const char *hook_name, feed_fn feed,
 		size_t n;
 		if (feed(feed_state, &buf, &n))
 			break;
-		if (write_in_full(proc.in, buf, n) != n)
+		if (write_in_full(proc.in, buf, n) < 0)
 			break;
 	}
 	close(proc.in);
diff --git a/builtin/rerere.c b/builtin/rerere.c
index ffb66e2907..0bc40298c2 100644
--- a/builtin/rerere.c
+++ b/builtin/rerere.c
@@ -18,7 +18,7 @@ static int outf(void *dummy, mmbuffer_t *ptr, int nbuf)
 {
 	int i;
 	for (i = 0; i < nbuf; i++)
-		if (write_in_full(1, ptr[i].ptr, ptr[i].size) != ptr[i].size)
+		if (write_in_full(1, ptr[i].ptr, ptr[i].size) < 0)
 			return -1;
 	return 0;
 }
diff --git a/builtin/unpack-file.c b/builtin/unpack-file.c
index 281ca1db6c..32e0155577 100644
--- a/builtin/unpack-file.c
+++ b/builtin/unpack-file.c
@@ -15,7 +15,7 @@ static char *create_temp_file(struct object_id *oid)
 
 	xsnprintf(path, sizeof(path), ".merge_file_XXXXXX");
 	fd = xmkstemp(path);
-	if (write_in_full(fd, buf, size) != size)
+	if (write_in_full(fd, buf, size) < 0)
 		die_errno("unable to write temp-file");
 	close(fd);
 	return path;
diff --git a/config.c b/config.c
index cd5a69e630..a77cae56ed 100644
--- a/config.c
+++ b/config.c
@@ -2292,10 +2292,11 @@ static int write_error(const char *filename)
 	return 4;
 }
 
-static int store_write_section(int fd, const char *key)
+static ssize_t write_section(int fd, const char *key)
 {
 	const char *dot;
-	int i, success;
+	int i;
+	ssize_t ret;
 	struct strbuf sb = STRBUF_INIT;
 
 	dot = memchr(key, '.', store.baselen);
@@ -2311,15 +2312,16 @@ static int store_write_section(int fd, const char *key)
 		strbuf_addf(&sb, "[%.*s]\n", store.baselen, key);
 	}
 
-	success = write_in_full(fd, sb.buf, sb.len) == sb.len;
+	ret = write_in_full(fd, sb.buf, sb.len);
 	strbuf_release(&sb);
 
-	return success;
+	return ret;
 }
 
-static int store_write_pair(int fd, const char *key, const char *value)
+static ssize_t write_pair(int fd, const char *key, const char *value)
 {
-	int i, success;
+	int i;
+	ssize_t ret;
 	int length = strlen(key + store.baselen + 1);
 	const char *quote = "";
 	struct strbuf sb = STRBUF_INIT;
@@ -2359,10 +2361,10 @@ static int store_write_pair(int fd, const char *key, const char *value)
 		}
 	strbuf_addf(&sb, "%s\n", quote);
 
-	success = write_in_full(fd, sb.buf, sb.len) == sb.len;
+	ret = write_in_full(fd, sb.buf, sb.len);
 	strbuf_release(&sb);
 
-	return success;
+	return ret;
 }
 
 static ssize_t find_beginning_of_line(const char *contents, size_t size,
@@ -2491,8 +2493,8 @@ int git_config_set_multivar_in_file_gently(const char *config_filename,
 		}
 
 		store.key = (char *)key;
-		if (!store_write_section(fd, key) ||
-		    !store_write_pair(fd, key, value))
+		if (write_section(fd, key) < 0 ||
+		    write_pair(fd, key, value) < 0)
 			goto write_err_out;
 	} else {
 		struct stat st;
@@ -2602,11 +2604,10 @@ int git_config_set_multivar_in_file_gently(const char *config_filename,
 			/* write the first part of the config */
 			if (copy_end > copy_begin) {
 				if (write_in_full(fd, contents + copy_begin,
-						  copy_end - copy_begin) <
-				    copy_end - copy_begin)
+						  copy_end - copy_begin) < 0)
 					goto write_err_out;
 				if (new_line &&
-				    write_str_in_full(fd, "\n") != 1)
+				    write_str_in_full(fd, "\n") < 0)
 					goto write_err_out;
 			}
 			copy_begin = store.offset[i];
@@ -2615,18 +2616,17 @@ int git_config_set_multivar_in_file_gently(const char *config_filename,
 		/* write the pair (value == NULL means unset) */
 		if (value != NULL) {
 			if (store.state == START) {
-				if (!store_write_section(fd, key))
+				if (write_section(fd, key) < 0)
 					goto write_err_out;
 			}
-			if (!store_write_pair(fd, key, value))
+			if (write_pair(fd, key, value) < 0)
 				goto write_err_out;
 		}
 
 		/* write the rest of the config */
 		if (copy_begin < contents_sz)
 			if (write_in_full(fd, contents + copy_begin,
-					  contents_sz - copy_begin) <
-			    contents_sz - copy_begin)
+					  contents_sz - copy_begin) < 0)
 				goto write_err_out;
 
 		munmap(contents, contents_sz);
@@ -2803,7 +2803,7 @@ int git_config_rename_section_in_file(const char *config_filename,
 					continue;
 				}
 				store.baselen = strlen(new_name);
-				if (!store_write_section(out_fd, new_name)) {
+				if (write_section(out_fd, new_name) < 0) {
 					ret = write_error(get_lock_file_path(lock));
 					goto out;
 				}
@@ -2829,7 +2829,7 @@ int git_config_rename_section_in_file(const char *config_filename,
 		if (remove)
 			continue;
 		length = strlen(output);
-		if (write_in_full(out_fd, output, length) != length) {
+		if (write_in_full(out_fd, output, length) < 0) {
 			ret = write_error(get_lock_file_path(lock));
 			goto out;
 		}
diff --git a/diff.c b/diff.c
index ea7e5978bc..3c6a3e0faa 100644
--- a/diff.c
+++ b/diff.c
@@ -3738,7 +3738,7 @@ static void prep_temp_blob(const char *path, struct diff_tempfile *temp,
 		blob = buf.buf;
 		size = buf.len;
 	}
-	if (write_in_full(temp->tempfile->fd, blob, size) != size ||
+	if (write_in_full(temp->tempfile->fd, blob, size) < 0 ||
 	    close_tempfile_gently(temp->tempfile))
 		die_errno("unable to write temp-file");
 	temp->name = get_tempfile_path(temp->tempfile);
diff --git a/entry.c b/entry.c
index cb291aa88b..1c7e3c11d5 100644
--- a/entry.c
+++ b/entry.c
@@ -257,7 +257,8 @@ static int write_entry(struct cache_entry *ce,
 	char *new;
 	struct strbuf buf = STRBUF_INIT;
 	unsigned long size;
-	size_t wrote, newsize = 0;
+	ssize_t wrote;
+	size_t newsize = 0;
 	struct stat st;
 	const struct submodule *sub;
 
@@ -332,7 +333,7 @@ static int write_entry(struct cache_entry *ce,
 			fstat_done = fstat_output(fd, state, &st);
 		close(fd);
 		free(new);
-		if (wrote != size)
+		if (wrote < 0)
 			return error("unable to write file %s", path);
 		break;
 	case S_IFGITLINK:
diff --git a/fast-import.c b/fast-import.c
index 49516d60e6..35bf671f12 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -2952,7 +2952,7 @@ static void parse_reset_branch(const char *arg)
 
 static void cat_blob_write(const char *buf, unsigned long size)
 {
-	if (write_in_full(cat_blob_fd, buf, size) != size)
+	if (write_in_full(cat_blob_fd, buf, size) < 0)
 		die_errno("Write to frontend failed");
 }
 
diff --git a/http-backend.c b/http-backend.c
index 8076b1d5e5..e51c7805c8 100644
--- a/http-backend.c
+++ b/http-backend.c
@@ -358,7 +358,7 @@ static void inflate_request(const char *prog_name, int out, int buffer_input)
 				die("zlib error inflating request, result %d", ret);
 
 			n = stream.total_out - cnt;
-			if (write_in_full(out, out_buf, n) != n)
+			if (write_in_full(out, out_buf, n) < 0)
 				die("%s aborted reading request", prog_name);
 			cnt += n;
 
@@ -379,7 +379,7 @@ static void copy_request(const char *prog_name, int out)
 	ssize_t n = read_request(0, &buf);
 	if (n < 0)
 		die_errno("error reading request body");
-	if (write_in_full(out, buf, n) != n)
+	if (write_in_full(out, buf, n) < 0)
 		die("%s aborted reading request", prog_name);
 	close(out);
 	free(buf);
diff --git a/ll-merge.c b/ll-merge.c
index 9fb855a900..a6ad2ec12d 100644
--- a/ll-merge.c
+++ b/ll-merge.c
@@ -154,7 +154,7 @@ static void create_temp(mmfile_t *src, char *path, size_t len)
 
 	xsnprintf(path, len, ".merge_file_XXXXXX");
 	fd = xmkstemp(path);
-	if (write_in_full(fd, src->ptr, src->size) != src->size)
+	if (write_in_full(fd, src->ptr, src->size) < 0)
 		die_errno("unable to write temp-file");
 	close(fd);
 }
diff --git a/notes-merge.c b/notes-merge.c
index b04d2f2131..597d43f65c 100644
--- a/notes-merge.c
+++ b/notes-merge.c
@@ -302,7 +302,7 @@ static void write_buf_to_worktree(const struct object_id *obj,
 	fd = xopen(path, O_WRONLY | O_EXCL | O_CREAT, 0666);
 
 	while (size > 0) {
-		long ret = write_in_full(fd, buf, size);
+		ssize_t ret = write_in_full(fd, buf, size);
 		if (ret < 0) {
 			/* Ignore epipe */
 			if (errno == EPIPE)
diff --git a/pkt-line.c b/pkt-line.c
index f364944b93..647bbd3bce 100644
--- a/pkt-line.c
+++ b/pkt-line.c
@@ -94,9 +94,9 @@ void packet_flush(int fd)
 int packet_flush_gently(int fd)
 {
 	packet_trace("0000", 4, 1);
-	if (write_in_full(fd, "0000", 4) == 4)
-		return 0;
-	return error("flush packet write failed");
+	if (write_in_full(fd, "0000", 4) < 0)
+		return error("flush packet write failed");
+	return 0;
 }
 
 void packet_buf_flush(struct strbuf *buf)
@@ -137,19 +137,18 @@ static int packet_write_fmt_1(int fd, int gently,
 			      const char *fmt, va_list args)
 {
 	static struct strbuf buf = STRBUF_INIT;
-	ssize_t count;
 
 	strbuf_reset(&buf);
 	format_packet(&buf, fmt, args);
-	count = write_in_full(fd, buf.buf, buf.len);
-	if (count == buf.len)
-		return 0;
-
-	if (!gently) {
-		check_pipe(errno);
-		die_errno("packet write with format failed");
+	if (write_in_full(fd, buf.buf, buf.len) < 0) {
+		if (!gently) {
+			check_pipe(errno);
+			die_errno("packet write with format failed");
+		}
+		return error("packet write with format failed");
 	}
-	return error("packet write with format failed");
+
+	return 0;
 }
 
 void packet_write_fmt(int fd, const char *fmt, ...)
@@ -184,9 +183,9 @@ static int packet_write_gently(const int fd_out, const char *buf, size_t size)
 	packet_size = size + 4;
 	set_packet_header(packet_write_buffer, packet_size);
 	memcpy(packet_write_buffer + 4, buf, size);
-	if (write_in_full(fd_out, packet_write_buffer, packet_size) == packet_size)
-		return 0;
-	return error("packet write failed");
+	if (write_in_full(fd_out, packet_write_buffer, packet_size) < 0)
+		return error("packet write failed");
+	return 0;
 }
 
 void packet_buf_write(struct strbuf *buf, const char *fmt, ...)
diff --git a/read-cache.c b/read-cache.c
index 7d00265c49..cdcd11c71e 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1922,7 +1922,7 @@ static int ce_write_flush(git_SHA_CTX *context, int fd)
 	unsigned int buffered = write_buffer_len;
 	if (buffered) {
 		git_SHA1_Update(context, write_buffer, buffered);
-		if (write_in_full(fd, write_buffer, buffered) != buffered)
+		if (write_in_full(fd, write_buffer, buffered) < 0)
 			return -1;
 		write_buffer_len = 0;
 	}
@@ -1971,7 +1971,7 @@ static int ce_flush(git_SHA_CTX *context, int fd, unsigned char *sha1)
 
 	/* Flush first if not enough space for SHA1 signature */
 	if (left + 20 > WRITE_BUFFER_SIZE) {
-		if (write_in_full(fd, write_buffer, left) != left)
+		if (write_in_full(fd, write_buffer, left) < 0)
 			return -1;
 		left = 0;
 	}
@@ -1980,7 +1980,7 @@ static int ce_flush(git_SHA_CTX *context, int fd, unsigned char *sha1)
 	git_SHA1_Final(write_buffer + left, context);
 	hashcpy(sha1, write_buffer + left);
 	left += 20;
-	return (write_in_full(fd, write_buffer, left) != left) ? -1 : 0;
+	return (write_in_full(fd, write_buffer, left) < 0) ? -1 : 0;
 }
 
 static void ce_smudge_racily_clean_entry(struct cache_entry *ce)
diff --git a/refs.c b/refs.c
index c30f4c36be..e8b67ddce8 100644
--- a/refs.c
+++ b/refs.c
@@ -609,7 +609,7 @@ static int write_pseudoref(const char *pseudoref, const unsigned char *sha1,
 		}
 	}
 
-	if (write_in_full(fd, buf.buf, buf.len) != buf.len) {
+	if (write_in_full(fd, buf.buf, buf.len) < 0) {
 		strbuf_addf(err, "could not write to '%s'", filename);
 		rollback_lock_file(&lock);
 		goto done;
diff --git a/refs/files-backend.c b/refs/files-backend.c
index 32663a999e..dac33628b3 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -1549,7 +1549,7 @@ static int log_ref_write_fd(int fd, const struct object_id *old_oid,
 
 	written = len <= maxlen ? write_in_full(fd, logrec, len) : -1;
 	free(logrec);
-	if (written != len)
+	if (written < 0)
 		return -1;
 
 	return 0;
@@ -1628,8 +1628,8 @@ static int write_ref_to_lockfile(struct ref_lock *lock,
 		return -1;
 	}
 	fd = get_lock_file_fd(&lock->lk);
-	if (write_in_full(fd, oid_to_hex(oid), GIT_SHA1_HEXSZ) != GIT_SHA1_HEXSZ ||
-	    write_in_full(fd, &term, 1) != 1 ||
+	if (write_in_full(fd, oid_to_hex(oid), GIT_SHA1_HEXSZ) < 0 ||
+	    write_in_full(fd, &term, 1) < 0 ||
 	    close_ref_gently(lock) < 0) {
 		strbuf_addf(err,
 			    "couldn't write '%s'", get_lock_file_path(&lock->lk));
@@ -3006,8 +3006,8 @@ static int files_reflog_expire(struct ref_store *ref_store,
 			rollback_lock_file(&reflog_lock);
 		} else if (update &&
 			   (write_in_full(get_lock_file_fd(&lock->lk),
-				oid_to_hex(&cb.last_kept_oid), GIT_SHA1_HEXSZ) != GIT_SHA1_HEXSZ ||
-			    write_str_in_full(get_lock_file_fd(&lock->lk), "\n") != 1 ||
+				oid_to_hex(&cb.last_kept_oid), GIT_SHA1_HEXSZ) < 0 ||
+			    write_str_in_full(get_lock_file_fd(&lock->lk), "\n") < 1 ||
 			    close_ref_gently(lock) < 0)) {
 			status |= error("couldn't write %s",
 					get_lock_file_path(&lock->lk));
diff --git a/rerere.c b/rerere.c
index d77235645e..1ce440f4bb 100644
--- a/rerere.c
+++ b/rerere.c
@@ -258,7 +258,7 @@ static int write_rr(struct string_list *rr, int out_fd)
 				    rerere_id_hex(id),
 				    rr->items[i].string, 0);
 
-		if (write_in_full(out_fd, buf.buf, buf.len) != buf.len)
+		if (write_in_full(out_fd, buf.buf, buf.len) < 0)
 			die("unable to write rerere record");
 
 		strbuf_release(&buf);
diff --git a/sha1_file.c b/sha1_file.c
index b4a67bb838..dd7cbe52ef 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1850,7 +1850,7 @@ int index_path(struct object_id *oid, const char *path, struct stat *st, unsigne
 
 int read_pack_header(int fd, struct pack_header *header)
 {
-	if (read_in_full(fd, header, sizeof(*header)) < sizeof(*header))
+	if (read_in_full(fd, header, sizeof(*header)) != sizeof(*header))
 		/* "eof before pack header was fully read" */
 		return PH_ERROR_EOF;
 
diff --git a/shallow.c b/shallow.c
index 1cc1c76415..eabb65d3a7 100644
--- a/shallow.c
+++ b/shallow.c
@@ -294,7 +294,7 @@ const char *setup_temporary_shallow(const struct oid_array *extra)
 	if (write_shallow_commits(&sb, 0, extra)) {
 		temp = xmks_tempfile(git_path("shallow_XXXXXX"));
 
-		if (write_in_full(temp->fd, sb.buf, sb.len) != sb.len ||
+		if (write_in_full(temp->fd, sb.buf, sb.len) < 0 ||
 		    close_tempfile_gently(temp) < 0)
 			die_errno("failed to write to %s",
 				  get_tempfile_path(temp));
@@ -319,7 +319,7 @@ void setup_alternate_shallow(struct lock_file *shallow_lock,
 				       LOCK_DIE_ON_ERROR);
 	check_shallow_file_for_update();
 	if (write_shallow_commits(&sb, 0, extra)) {
-		if (write_in_full(fd, sb.buf, sb.len) != sb.len)
+		if (write_in_full(fd, sb.buf, sb.len) < 0)
 			die_errno("failed to write to %s",
 				  get_lock_file_path(shallow_lock));
 		*alternate_shallow_file = get_lock_file_path(shallow_lock);
@@ -366,7 +366,7 @@ void prune_shallow(int show_only)
 				       LOCK_DIE_ON_ERROR);
 	check_shallow_file_for_update();
 	if (write_shallow_commits_1(&sb, 0, NULL, SEEN_ONLY)) {
-		if (write_in_full(fd, sb.buf, sb.len) != sb.len)
+		if (write_in_full(fd, sb.buf, sb.len) < 0)
 			die_errno("failed to write to %s",
 				  get_lock_file_path(&shallow_lock));
 		commit_lock_file(&shallow_lock);
diff --git a/streaming.c b/streaming.c
index 6f1c60f12b..5892b50bd8 100644
--- a/streaming.c
+++ b/streaming.c
@@ -540,7 +540,7 @@ int stream_blob_to_fd(int fd, const struct object_id *oid, struct stream_filter
 			kept = 0;
 		wrote = write_in_full(fd, buf, readlen);
 
-		if (wrote != readlen)
+		if (wrote < 0)
 			goto close_and_exit;
 	}
 	if (kept && (lseek(fd, kept - 1, SEEK_CUR) == (off_t) -1 ||
diff --git a/t/helper/test-delta.c b/t/helper/test-delta.c
index 59937dc1be..591730adc4 100644
--- a/t/helper/test-delta.c
+++ b/t/helper/test-delta.c
@@ -69,7 +69,7 @@ int cmd_main(int argc, const char **argv)
 	}
 
 	fd = open (argv[4], O_WRONLY|O_CREAT|O_TRUNC, 0666);
-	if (fd < 0 || write_in_full(fd, out_buf, out_size) != out_size) {
+	if (fd < 0 || write_in_full(fd, out_buf, out_size) < 0) {
 		perror(argv[4]);
 		return 1;
 	}
diff --git a/transport-helper.c b/transport-helper.c
index 42b960ff86..c948d5215c 100644
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -44,8 +44,7 @@ static void sendline(struct helper_data *helper, struct strbuf *buffer)
 {
 	if (debug)
 		fprintf(stderr, "Debug: Remote helper: -> %s", buffer->buf);
-	if (write_in_full(helper->helper->in, buffer->buf, buffer->len)
-		!= buffer->len)
+	if (write_in_full(helper->helper->in, buffer->buf, buffer->len) < 0)
 		die_errno("Full write to remote helper failed");
 }
 
@@ -74,7 +73,7 @@ static void write_constant(int fd, const char *str)
 {
 	if (debug)
 		fprintf(stderr, "Debug: Remote helper: -> %s", str);
-	if (write_in_full(fd, str, strlen(str)) != strlen(str))
+	if (write_in_full(fd, str, strlen(str)) < 0)
 		die_errno("Full write to remote helper failed");
 }
 
diff --git a/wrapper.c b/wrapper.c
index 36630e5d18..61aba0b5c1 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -652,7 +652,7 @@ int xsnprintf(char *dst, size_t max, const char *fmt, ...)
 void write_file_buf(const char *path, const char *buf, size_t len)
 {
 	int fd = xopen(path, O_WRONLY | O_CREAT | O_TRUNC, 0666);
-	if (write_in_full(fd, buf, len) != len)
+	if (write_in_full(fd, buf, len) < 0)
 		die_errno(_("could not write to %s"), path);
 	if (close(fd))
 		die_errno(_("could not close %s"), path);