diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines
index 9d5c27807a..003393ed16 100644
--- a/Documentation/CodingGuidelines
+++ b/Documentation/CodingGuidelines
@@ -442,8 +442,12 @@ For C programs:
    detail.
 
  - The first #include in C files, except in platform specific compat/
-   implementations, must be either "git-compat-util.h", "cache.h" or
-   "builtin.h".  You do not have to include more than one of these.
+   implementations and sha1dc/, must be either "git-compat-util.h" or
+   one of the approved headers that includes it first for you.  (The
+   approved headers currently include "cache.h", "builtin.h",
+   "t/helper/test-tool.h", "xdiff/xinclude.h", or
+   "reftable/system.h").  You do not have to include more than one of
+   these.
 
  - A C file must directly include the header files that declare the
    functions and the types it uses, except for the functions and types
diff --git a/cbtree.c b/cbtree.c
index 336e46dbba..c1cc30a5dc 100644
--- a/cbtree.c
+++ b/cbtree.c
@@ -4,6 +4,7 @@
  * Based on Adam Langley's adaptation of Dan Bernstein's public domain code
  * git clone https://github.com/agl/critbit.git
  */
+#include "git-compat-util.h"
 #include "cbtree.h"
 
 static struct cb_node *cb_node_of(const void *p)
diff --git a/compat/fsmonitor/fsm-ipc-win32.c b/compat/fsmonitor/fsm-ipc-win32.c
index e08c505c14..c9536dfb66 100644
--- a/compat/fsmonitor/fsm-ipc-win32.c
+++ b/compat/fsmonitor/fsm-ipc-win32.c
@@ -1,3 +1,4 @@
+#include "git-compat-util.h"
 #include "config.h"
 #include "fsmonitor-ipc.h"
 
diff --git a/compat/fsmonitor/fsm-settings-darwin.c b/compat/fsmonitor/fsm-settings-darwin.c
index 6abbc7af3a..58b623fbb9 100644
--- a/compat/fsmonitor/fsm-settings-darwin.c
+++ b/compat/fsmonitor/fsm-settings-darwin.c
@@ -1,3 +1,4 @@
+#include "git-compat-util.h"
 #include "config.h"
 #include "fsmonitor.h"
 #include "fsmonitor-ipc.h"
diff --git a/diff-merges.c b/diff-merges.c
index 85cbefa5af..faa7bc73a3 100644
--- a/diff-merges.c
+++ b/diff-merges.c
@@ -1,3 +1,4 @@
+#include "git-compat-util.h"
 #include "diff-merges.h"
 
 #include "revision.h"
diff --git a/fmt-merge-msg.c b/fmt-merge-msg.c
index f48f44f9cd..f317f12990 100644
--- a/fmt-merge-msg.c
+++ b/fmt-merge-msg.c
@@ -1,3 +1,4 @@
+#include "git-compat-util.h"
 #include "config.h"
 #include "refs.h"
 #include "object-store.h"
diff --git a/oidtree.c b/oidtree.c
index 0d39389bee..7d57b7b19e 100644
--- a/oidtree.c
+++ b/oidtree.c
@@ -2,6 +2,7 @@
  * A wrapper around cbtree which stores oids
  * May be used to replace oid-array for prefix (abbreviation) matches
  */
+#include "git-compat-util.h"
 #include "oidtree.h"
 #include "alloc.h"
 #include "hash.h"
diff --git a/oss-fuzz/fuzz-commit-graph.c b/oss-fuzz/fuzz-commit-graph.c
index 914026f5d8..2992079dd9 100644
--- a/oss-fuzz/fuzz-commit-graph.c
+++ b/oss-fuzz/fuzz-commit-graph.c
@@ -1,3 +1,4 @@
+#include "git-compat-util.h"
 #include "commit-graph.h"
 #include "repository.h"
 
diff --git a/oss-fuzz/fuzz-pack-headers.c b/oss-fuzz/fuzz-pack-headers.c
index 99da1d0fd3..150c0f5fa2 100644
--- a/oss-fuzz/fuzz-pack-headers.c
+++ b/oss-fuzz/fuzz-pack-headers.c
@@ -1,3 +1,4 @@
+#include "git-compat-util.h"
 #include "packfile.h"
 
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
diff --git a/oss-fuzz/fuzz-pack-idx.c b/oss-fuzz/fuzz-pack-idx.c
index 0c3d777aac..609a343ee3 100644
--- a/oss-fuzz/fuzz-pack-idx.c
+++ b/oss-fuzz/fuzz-pack-idx.c
@@ -1,3 +1,4 @@
+#include "git-compat-util.h"
 #include "object-store.h"
 #include "packfile.h"
 
diff --git a/prune-packed.c b/prune-packed.c
index 261520b472..d2813f6a40 100644
--- a/prune-packed.c
+++ b/prune-packed.c
@@ -1,3 +1,4 @@
+#include "git-compat-util.h"
 #include "object-store.h"
 #include "packfile.h"
 #include "progress.h"
diff --git a/rebase.c b/rebase.c
index 6775cddb28..17a570f1ff 100644
--- a/rebase.c
+++ b/rebase.c
@@ -1,3 +1,4 @@
+#include "git-compat-util.h"
 #include "rebase.h"
 #include "config.h"
 #include "gettext.h"
diff --git a/refs/debug.c b/refs/debug.c
index eed8bc94b0..ff7766bc63 100644
--- a/refs/debug.c
+++ b/refs/debug.c
@@ -1,4 +1,4 @@
-
+#include "git-compat-util.h"
 #include "refs-internal.h"
 #include "trace.h"
 
diff --git a/sub-process.c b/sub-process.c
index 6d4232294d..1daf5a9752 100644
--- a/sub-process.c
+++ b/sub-process.c
@@ -1,6 +1,7 @@
 /*
  * Generic implementation of background process infrastructure.
  */
+#include "git-compat-util.h"
 #include "sub-process.h"
 #include "sigchain.h"
 #include "pkt-line.h"