diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index ca7784dc2c..bb3639641c 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -145,8 +145,7 @@ static int check_self_contained_and_connected;
 
 static struct progress *progress;
 
-/* We always read in 4kB chunks. */
-static unsigned char input_buffer[4096];
+static unsigned char input_buffer[DEFAULT_IO_BUFFER_SIZE];
 static unsigned int input_offset, input_len;
 static off_t consumed_bytes;
 static off_t max_input_size;
diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c
index e01cf6e360..af67d1a1d3 100644
--- a/builtin/unpack-objects.c
+++ b/builtin/unpack-objects.c
@@ -23,8 +23,7 @@
 static int dry_run, quiet, recover, has_errors, strict;
 static const char unpack_usage[] = "git unpack-objects [-n] [-q] [-r] [--strict]";
 
-/* We always read in 4kB chunks. */
-static unsigned char buffer[4096];
+static unsigned char buffer[DEFAULT_IO_BUFFER_SIZE];
 static unsigned int offset, len;
 static off_t consumed_bytes;
 static off_t max_input_size;
diff --git a/csum-file.c b/csum-file.c
index 9558177a11..d7a682c2b6 100644
--- a/csum-file.c
+++ b/csum-file.c
@@ -178,7 +178,7 @@ struct hashfile *hashfd_ext(const struct git_hash_algo *algop,
 	f->algop = unsafe_hash_algo(algop);
 	f->algop->init_fn(&f->ctx);
 
-	f->buffer_len = opts->buffer_len ? opts->buffer_len : 128 * 1024;
+	f->buffer_len = opts->buffer_len ? opts->buffer_len : DEFAULT_IO_BUFFER_SIZE;
 	f->buffer = xmalloc(f->buffer_len);
 	f->check_buffer = NULL;
 
diff --git a/git-compat-util.h b/git-compat-util.h
index ae1bdc90a4..5024814bd4 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -712,6 +712,12 @@ static inline uint64_t u64_add(uint64_t a, uint64_t b)
 # endif
 #endif
 
+/*
+ * Default buffer size for buffered I/O in index-pack, unpack-objects,
+ * and the hashfile layer in csum-file.
+ */
+#define DEFAULT_IO_BUFFER_SIZE (128 * 1024)
+
 #ifdef HAVE_ALLOCA_H
 # include <alloca.h>
 # define xalloca(size)      (alloca(size))