diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines
index ccaea39752..d0fc7cfe60 100644
--- a/Documentation/CodingGuidelines
+++ b/Documentation/CodingGuidelines
@@ -258,6 +258,13 @@ For C programs:
    ensure your patch is clear of all compiler warnings we care about,
    by e.g. "echo DEVELOPER=1 >>config.mak".
 
+ - When using DEVELOPER=1 mode, you may see warnings from the compiler
+   like "error: unused parameter 'foo' [-Werror=unused-parameter]",
+   which indicates that a function ignores its argument. If the unused
+   parameter can't be removed (e.g., because the function is used as a
+   callback and has to match a certain interface), you can annotate the
+   individual parameters with the UNUSED keyword, like "int foo UNUSED".
+
  - We try to support a wide range of C compilers to compile Git with,
    including old ones.  As of Git v2.35.0 Git requires C99 (we check
    "__STDC_VERSION__"). You should not use features from a newer C
diff --git a/builtin/gc.c b/builtin/gc.c
index 427faf1cfe..0e361253e3 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -967,7 +967,7 @@ static int dfs_on_ref(const char *refname UNUSED,
 	return result;
 }
 
-static int should_write_commit_graph(struct gc_config *cfg)
+static int should_write_commit_graph(struct gc_config *cfg UNUSED)
 {
 	int result;
 	struct cg_auto_data data;
@@ -1005,7 +1005,7 @@ static int run_write_commit_graph(struct maintenance_run_opts *opts)
 }
 
 static int maintenance_task_commit_graph(struct maintenance_run_opts *opts,
-					 struct gc_config *cfg)
+					 struct gc_config *cfg UNUSED)
 {
 	prepare_repo_settings(the_repository);
 	if (!the_repository->settings.core_commit_graph)
@@ -1040,7 +1040,7 @@ static int fetch_remote(struct remote *remote, void *cbdata)
 }
 
 static int maintenance_task_prefetch(struct maintenance_run_opts *opts,
-				     struct gc_config *cfg)
+				     struct gc_config *cfg UNUSED)
 {
 	if (for_each_remote(fetch_remote, opts)) {
 		error(_("failed to prefetch remotes"));
@@ -1051,7 +1051,7 @@ static int maintenance_task_prefetch(struct maintenance_run_opts *opts,
 }
 
 static int maintenance_task_gc(struct maintenance_run_opts *opts,
-			       struct gc_config *cfg)
+			       struct gc_config *cfg UNUSED)
 {
 	struct child_process child = CHILD_PROCESS_INIT;
 
@@ -1100,7 +1100,7 @@ static int loose_object_count(const struct object_id *oid UNUSED,
 	return 0;
 }
 
-static int loose_object_auto_condition(struct gc_config *cfg)
+static int loose_object_auto_condition(struct gc_config *cfg UNUSED)
 {
 	int count = 0;
 
@@ -1192,12 +1192,12 @@ static int pack_loose(struct maintenance_run_opts *opts)
 }
 
 static int maintenance_task_loose_objects(struct maintenance_run_opts *opts,
-					  struct gc_config *cfg)
+					  struct gc_config *cfg UNUSED)
 {
 	return prune_packed(opts) || pack_loose(opts);
 }
 
-static int incremental_repack_auto_condition(struct gc_config *cfg)
+static int incremental_repack_auto_condition(struct gc_config *cfg UNUSED)
 {
 	struct packed_git *p;
 	int incremental_repack_auto_limit = 10;
@@ -1317,7 +1317,7 @@ static int multi_pack_index_repack(struct maintenance_run_opts *opts)
 }
 
 static int maintenance_task_incremental_repack(struct maintenance_run_opts *opts,
-					       struct gc_config *cfg)
+					       struct gc_config *cfg UNUSED)
 {
 	prepare_repo_settings(the_repository);
 	if (!the_repository->settings.core_multi_pack_index) {
diff --git a/compat/mingw.c b/compat/mingw.c
index 29d3f09768..eb13c02a76 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -243,7 +243,8 @@ static enum hide_dotfiles_type hide_dotfiles = HIDE_DOTFILES_DOTGITONLY;
 static char *unset_environment_variables;
 
 int mingw_core_config(const char *var, const char *value,
-		      const struct config_context *ctx, void *cb)
+		      const struct config_context *ctx UNUSED,
+		      void *cb UNUSED)
 {
 	if (!strcmp(var, "core.hidedotfiles")) {
 		if (value && !strcasecmp(value, "dotgitonly"))
@@ -453,7 +454,7 @@ static int set_hidden_flag(const wchar_t *path, int set)
 	return -1;
 }
 
-int mingw_mkdir(const char *path, int mode)
+int mingw_mkdir(const char *path, int mode UNUSED)
 {
 	int ret;
 	wchar_t wpath[MAX_PATH];
@@ -597,7 +598,7 @@ int mingw_open (const char *filename, int oflags, ...)
 	return fd;
 }
 
-static BOOL WINAPI ctrl_ignore(DWORD type)
+static BOOL WINAPI ctrl_ignore(DWORD type UNUSED)
 {
 	return TRUE;
 }
@@ -1085,7 +1086,7 @@ int mkstemp(char *template)
 	return git_mkstemp_mode(template, 0600);
 }
 
-int gettimeofday(struct timeval *tv, void *tz)
+int gettimeofday(struct timeval *tv, void *tz UNUSED)
 {
 	FILETIME ft;
 	long long hnsec;
@@ -2252,7 +2253,7 @@ char *mingw_query_user_email(void)
 	return get_extended_user_info(NameUserPrincipal);
 }
 
-struct passwd *getpwuid(int uid)
+struct passwd *getpwuid(int uid UNUSED)
 {
 	static unsigned initialized;
 	static char user_name[100];
@@ -2304,7 +2305,7 @@ static sig_handler_t timer_fn = SIG_DFL, sigint_fn = SIG_DFL;
  * length to call the signal handler.
  */
 
-static unsigned __stdcall ticktack(void *dummy)
+static unsigned __stdcall ticktack(void *dummy UNUSED)
 {
 	while (WaitForSingleObject(timer_event, timer_interval) == WAIT_TIMEOUT) {
 		mingw_raise(SIGALRM);
@@ -2352,7 +2353,7 @@ static inline int is_timeval_eq(const struct timeval *i1, const struct timeval *
 	return i1->tv_sec == i2->tv_sec && i1->tv_usec == i2->tv_usec;
 }
 
-int setitimer(int type, struct itimerval *in, struct itimerval *out)
+int setitimer(int type UNUSED, struct itimerval *in, struct itimerval *out)
 {
 	static const struct timeval zero;
 	static int atexit_done;
diff --git a/compat/mingw.h b/compat/mingw.h
index 27b61284f4..ebfb8ba423 100644
--- a/compat/mingw.h
+++ b/compat/mingw.h
@@ -122,17 +122,17 @@ struct utsname {
  * trivial stubs
  */
 
-static inline int readlink(const char *path, char *buf, size_t bufsiz)
+static inline int readlink(const char *path UNUSED, char *buf UNUSED, size_t bufsiz UNUSED)
 { errno = ENOSYS; return -1; }
-static inline int symlink(const char *oldpath, const char *newpath)
+static inline int symlink(const char *oldpath UNUSED, const char *newpath UNUSED)
 { errno = ENOSYS; return -1; }
-static inline int fchmod(int fildes, mode_t mode)
+static inline int fchmod(int fildes UNUSED, mode_t mode UNUSED)
 { errno = ENOSYS; return -1; }
 #ifndef __MINGW64_VERSION_MAJOR
 static inline pid_t fork(void)
 { errno = ENOSYS; return -1; }
 #endif
-static inline unsigned int alarm(unsigned int seconds)
+static inline unsigned int alarm(unsigned int seconds UNUSED)
 { return 0; }
 static inline int fsync(int fd)
 { return _commit(fd); }
@@ -140,9 +140,9 @@ static inline void sync(void)
 {}
 static inline uid_t getuid(void)
 { return 1; }
-static inline struct passwd *getpwnam(const char *name)
+static inline struct passwd *getpwnam(const char *name UNUSED)
 { return NULL; }
-static inline int fcntl(int fd, int cmd, ...)
+static inline int fcntl(int fd UNUSED, int cmd, ...)
 {
 	if (cmd == F_GETFD || cmd == F_SETFD)
 		return 0;
@@ -151,17 +151,17 @@ static inline int fcntl(int fd, int cmd, ...)
 }
 
 #define sigemptyset(x) (void)0
-static inline int sigaddset(sigset_t *set, int signum)
+static inline int sigaddset(sigset_t *set UNUSED, int signum UNUSED)
 { return 0; }
 #define SIG_BLOCK 0
 #define SIG_UNBLOCK 0
-static inline int sigprocmask(int how, const sigset_t *set, sigset_t *oldset)
+static inline int sigprocmask(int how UNUSED, const sigset_t *set UNUSED, sigset_t *oldset UNUSED)
 { return 0; }
 static inline pid_t getppid(void)
 { return 1; }
 static inline pid_t getpgid(pid_t pid)
 { return pid == 0 ? getpid() : pid; }
-static inline pid_t tcgetpgrp(int fd)
+static inline pid_t tcgetpgrp(int fd UNUSED)
 { return getpid(); }
 
 /*
diff --git a/compat/nedmalloc/nedmalloc.c b/compat/nedmalloc/nedmalloc.c
index 2c0ace7075..145255da43 100644
--- a/compat/nedmalloc/nedmalloc.c
+++ b/compat/nedmalloc/nedmalloc.c
@@ -31,6 +31,8 @@ DEALINGS IN THE SOFTWARE.
 /*#pragma optimize("a", on)*/
 #endif
 
+#pragma GCC diagnostic ignored "-Wunused-parameter"
+
 /*#define FULLSANITYCHECKS*/
 
 #include "nedmalloc.h"
diff --git a/compat/regex/regcomp.c b/compat/regex/regcomp.c
index 6c5d455e92..8d93a9b93f 100644
--- a/compat/regex/regcomp.c
+++ b/compat/regex/regcomp.c
@@ -17,6 +17,8 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
+#pragma GCC diagnostic ignored "-Wunused-parameter"
+
 #if defined __TANDEM
  /* This is currently duplicated from git-compat-utils.h */
 # ifdef NO_INTPTR_T
diff --git a/compat/stub/procinfo.c b/compat/stub/procinfo.c
index 12c0a23c9e..3168cd5714 100644
--- a/compat/stub/procinfo.c
+++ b/compat/stub/procinfo.c
@@ -6,6 +6,6 @@
  * Stub. See sample implementations in compat/linux/procinfo.c and
  * compat/win32/trace2_win32_process_info.c.
  */
-void trace2_collect_process_info(enum trace2_process_info_reason reason)
+void trace2_collect_process_info(enum trace2_process_info_reason reason UNUSED)
 {
 }
diff --git a/compat/win32/headless.c b/compat/win32/headless.c
index 8b00dfe3bd..11392a0b9a 100644
--- a/compat/win32/headless.c
+++ b/compat/win32/headless.c
@@ -11,6 +11,8 @@
 #include <stdlib.h>
 #include <wchar.h>
 
+#pragma GCC diagnostic ignored "-Wunused-parameter"
+
 /*
  * If `dir` contains the path to a Git exec directory, extend `PATH` to
  * include the corresponding `bin/` directory (which is where all those
diff --git a/compat/win32/pthread.c b/compat/win32/pthread.c
index 85f8f7920c..58980a529c 100644
--- a/compat/win32/pthread.c
+++ b/compat/win32/pthread.c
@@ -21,7 +21,7 @@ static unsigned __stdcall win32_start_routine(void *arg)
 	return 0;
 }
 
-int pthread_create(pthread_t *thread, const void *unused,
+int pthread_create(pthread_t *thread, const void *attr UNUSED,
 		   void *(*start_routine)(void *), void *arg)
 {
 	thread->arg = arg;
diff --git a/compat/win32/pthread.h b/compat/win32/pthread.h
index cc3221cb2c..e2b5c4f64c 100644
--- a/compat/win32/pthread.h
+++ b/compat/win32/pthread.h
@@ -18,7 +18,7 @@
  */
 #define pthread_mutex_t CRITICAL_SECTION
 
-static inline int return_0(int i) {
+static inline int return_0(int i UNUSED) {
 	return 0;
 }
 #define pthread_mutex_init(a,b) return_0((InitializeCriticalSection((a)), 0))
@@ -70,7 +70,7 @@ static inline void NORETURN pthread_exit(void *ret)
 }
 
 typedef DWORD pthread_key_t;
-static inline int pthread_key_create(pthread_key_t *keyp, void (*destructor)(void *value))
+static inline int pthread_key_create(pthread_key_t *keyp, void (*destructor)(void *value) UNUSED)
 {
 	return (*keyp = TlsAlloc()) == TLS_OUT_OF_INDEXES ? EAGAIN : 0;
 }
diff --git a/compat/win32/syslog.c b/compat/win32/syslog.c
index 0af18d8882..4e4794743a 100644
--- a/compat/win32/syslog.c
+++ b/compat/win32/syslog.c
@@ -2,7 +2,7 @@
 
 static HANDLE ms_eventlog;
 
-void openlog(const char *ident, int logopt, int facility)
+void openlog(const char *ident, int logopt UNUSED, int facility UNUSED)
 {
 	if (ms_eventlog)
 		return;
diff --git a/compat/win32mmap.c b/compat/win32mmap.c
index 519d51f2b6..a4ab4cb939 100644
--- a/compat/win32mmap.c
+++ b/compat/win32mmap.c
@@ -40,7 +40,7 @@ void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t of
 	return MAP_FAILED;
 }
 
-int git_munmap(void *start, size_t length)
+int git_munmap(void *start, size_t length UNUSED)
 {
 	return !UnmapViewOfFile(start);
 }
diff --git a/compat/winansi.c b/compat/winansi.c
index 575813bde8..1b3f916b9f 100644
--- a/compat/winansi.c
+++ b/compat/winansi.c
@@ -340,7 +340,7 @@ enum {
 	TEXT = 0, ESCAPE = 033, BRACKET = '['
 };
 
-static DWORD WINAPI console_thread(LPVOID unused)
+static DWORD WINAPI console_thread(LPVOID data UNUSED)
 {
 	unsigned char buffer[BUFFER_SIZE];
 	DWORD bytes;
diff --git a/config.mak.dev b/config.mak.dev
index 5229c35484..50026d1e0e 100644
--- a/config.mak.dev
+++ b/config.mak.dev
@@ -54,7 +54,6 @@ ifeq ($(filter extra-all,$(DEVOPTS)),)
 DEVELOPER_CFLAGS += -Wno-empty-body
 DEVELOPER_CFLAGS += -Wno-missing-field-initializers
 DEVELOPER_CFLAGS += -Wno-sign-compare
-DEVELOPER_CFLAGS += -Wno-unused-parameter
 endif
 endif
 
diff --git a/t/unit-tests/t-reftable-readwrite.c b/t/unit-tests/t-reftable-readwrite.c
index 1eae36cc60..178296891c 100644
--- a/t/unit-tests/t-reftable-readwrite.c
+++ b/t/unit-tests/t-reftable-readwrite.c
@@ -26,7 +26,7 @@ static ssize_t strbuf_add_void(void *b, const void *data, size_t sz)
 	return sz;
 }
 
-static int noop_flush(void *arg)
+static int noop_flush(void *arg UNUSED)
 {
 	return 0;
 }