diff --git a/Documentation/config/core.adoc b/Documentation/config/core.adoc
index 340329edc3..33104444ab 100644
--- a/Documentation/config/core.adoc
+++ b/Documentation/config/core.adoc
@@ -118,6 +118,12 @@ core.trustctime::
 	crawlers and some backup systems).
 	See linkgit:git-update-index[1]. True by default.
 
+core.useNanosec::
+	If true, use nanosecond precision for ctime and mtime
+	comparisions between the index and the working tree (if Git
+	was compiled to store it).
+	See link:technical/racy-git.html[Racy Git]. False by default.
+
 core.splitIndex::
 	If true, the split-index feature of the index will be used.
 	See linkgit:git-update-index[1]. False by default.
diff --git a/Documentation/technical/racy-git.adoc b/Documentation/technical/racy-git.adoc
index 59bea66c0f..499231585b 100644
--- a/Documentation/technical/racy-git.adoc
+++ b/Documentation/technical/racy-git.adoc
@@ -39,8 +39,8 @@ files) from `st_mode` member, `st_mtime` and `st_ctime`
 timestamps, `st_uid`, `st_gid`, `st_ino`, and `st_size` members.
 With a `USE_STDEV` compile-time option, `st_dev` is also
 compared, but this is not enabled by default because this member
-is not stable on network filesystems.  With `USE_NSEC`
-compile-time option, `st_mtim.tv_nsec` and `st_ctim.tv_nsec`
+is not stable on network filesystems.  With 'core.useNanosec'
+config setting, `st_mtim.tv_nsec` and `st_ctim.tv_nsec`
 members are also compared. On Linux, this is not enabled by default
 because in-core timestamps can have finer granularity than
 on-disk timestamps, resulting in meaningless changes when an
@@ -49,9 +49,10 @@ of git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
 ([PATCH] Sync in core time granularity with filesystems,
 2005-01-04). This patch is included in kernel 2.6.11 and newer, but
 only fixes the issue for file systems with exactly 1 ns or 1 s
-resolution. Other file systems are still broken in current Linux
-kernels (e.g. CEPH, CIFS, NTFS, UDF), see
-https://lore.kernel.org/lkml/5577240D.7020309@gmail.com/
+resolution.  As of kernel 4.3, other file systems (CEPH, CIFS, NTFS, UFS, FUSE)
+were fixed; see https://public-inbox.org/git/5605D88A.20104%40gmail.com/.  FAT
+has been fixed since 2015.  The usual suspects (ext2, ext4, XFS) are known to
+work, too.
 
 Racy Git
 --------
diff --git a/Makefile b/Makefile
index fac3e8879c..b4ebcb9e83 100644
--- a/Makefile
+++ b/Makefile
@@ -197,18 +197,11 @@ include shared.mak
 # Define NO_NORETURN if using buggy versions of gcc 4.6+ and profile feedback,
 # as the compiler can crash (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49299)
 #
-# Define USE_NSEC below if you want git to care about sub-second file mtimes
-# and ctimes. Note that you need recent glibc (at least 2.2.4) for this. On
-# Linux, kernel 2.6.11 or newer is required for reliable sub-second file times
-# on file systems with exactly 1 ns or 1 s resolution. If you intend to use Git
-# on other file systems (e.g. CEPH, CIFS, NTFS, UDF), don't enable USE_NSEC. See
-# Documentation/technical/racy-git.adoc for details.
-#
 # Define USE_ST_TIMESPEC if your "struct stat" uses "st_ctimespec" instead of
 # "st_ctim"
 #
 # Define NO_NSEC if your "struct stat" does not have "st_ctim.tv_nsec"
-# available.  This automatically turns USE_NSEC off.
+# available.
 #
 # Define USE_STDEV below if you want git to care about the underlying device
 # change being considered an inode change from the update-index perspective.
@@ -1935,9 +1928,6 @@ endif
 ifdef NO_ST_BLOCKS_IN_STRUCT_STAT
 	BASIC_CFLAGS += -DNO_ST_BLOCKS_IN_STRUCT_STAT
 endif
-ifdef USE_NSEC
-	BASIC_CFLAGS += -DUSE_NSEC
-endif
 ifdef USE_ST_TIMESPEC
 	BASIC_CFLAGS += -DUSE_ST_TIMESPEC
 endif
diff --git a/builtin/update-index.c b/builtin/update-index.c
index 241abd4332..8e0c25655f 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -130,7 +130,7 @@ static void xrmdir(const char *path)
 static void avoid_racy(void)
 {
 	/*
-	 * not use if we could usleep(10) if USE_NSEC is defined. The
+	 * not use if we could usleep(10) if core.useNanosec is defined. The
 	 * field nsec could be there, but the OS could choose to
 	 * ignore it?
 	 */
diff --git a/compat/posix.h b/compat/posix.h
index e2e794cad7..51ee03233b 100644
--- a/compat/posix.h
+++ b/compat/posix.h
@@ -487,7 +487,6 @@ int git_qsort_s(void *base, size_t nmemb, size_t size,
 } while (0)
 
 #ifdef NO_NSEC
-#undef USE_NSEC
 #define ST_CTIME_NSEC(st) 0
 #define ST_MTIME_NSEC(st) 0
 #else
diff --git a/configure.ac b/configure.ac
index cfb50112bf..fc956776ab 100644
--- a/configure.ac
+++ b/configure.ac
@@ -351,12 +351,6 @@ GIT_PARSE_WITH(iconv))
 
 ## --enable-FEATURE[=ARG] and --disable-FEATURE
 #
-# Define USE_NSEC below if you want git to care about sub-second file mtimes
-# and ctimes. Note that you need recent glibc (at least 2.2.4) for this, and
-# it will BREAK YOUR LOCAL DIFFS! show-diff and anything using it will likely
-# randomly break unless your underlying filesystem supports those sub-second
-# times (my ext3 doesn't).
-#
 # Define USE_STDEV below if you want git to care about the underlying device
 # change being considered an inode change from the update-index perspective.
 
diff --git a/environment.c b/environment.c
index 6676e6f5ae..e6a50060e8 100644
--- a/environment.c
+++ b/environment.c
@@ -571,6 +571,11 @@ int git_default_core_config(const char *var, const char *value,
 		return 0;
 	}
 
+	if (!strcmp(var, "core.usenanosec")) {
+		cfg->use_nanosec = git_config_bool(var, value);
+		return 0;
+	}
+
 	/* Add other config variables here and to Documentation/config.adoc. */
 	return platform_core_config(var, value, ctx, cb);
 }
@@ -769,6 +774,7 @@ void repo_config_values_init(struct repo_config_values *cfg)
 	cfg->ignore_case = 0;
 	cfg->trust_executable_bit = 1;
 	cfg->has_symlinks = platform_has_symlinks();
+	cfg->use_nanosec = 0;
 
 	/* section "sparse" config values */
 	cfg->sparse_expect_files_outside_of_patterns = 0;
diff --git a/environment.h b/environment.h
index e7ec5b0437..a35534afe5 100644
--- a/environment.h
+++ b/environment.h
@@ -139,6 +139,7 @@ struct repo_config_values {
 	int ignore_case;
 	int trust_executable_bit;
 	int has_symlinks;
+	int use_nanosec;
 
 	/* section "sparse" config values */
 	int sparse_expect_files_outside_of_patterns;
diff --git a/read-cache.c b/read-cache.c
index 6c449f393d..297646c357 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -353,15 +353,16 @@ static int ce_match_stat_basic(const struct cache_entry *ce, struct stat *st)
 static int is_racy_stat(const struct index_state *istate,
 			const struct stat_data *sd)
 {
+	int use_nsec = 0;
+	repo_config_get_bool(the_repository, "core.useNanosec", &use_nsec);
+
 	return (istate->timestamp.sec &&
-#ifdef USE_NSEC
-		 /* nanosecond timestamped files can also be racy! */
-		(istate->timestamp.sec < sd->sd_mtime.sec ||
-		 (istate->timestamp.sec == sd->sd_mtime.sec &&
-		  istate->timestamp.nsec <= sd->sd_mtime.nsec))
-#else
-		istate->timestamp.sec <= sd->sd_mtime.sec
-#endif
+		/* nanosecond timestamped files can also be racy! */
+		use_nsec
+		? (istate->timestamp.sec < sd->sd_mtime.sec ||
+		   (istate->timestamp.sec == sd->sd_mtime.sec &&
+		    istate->timestamp.nsec <= sd->sd_mtime.nsec))
+		: istate->timestamp.sec <= sd->sd_mtime.sec
 		);
 }
 
diff --git a/statinfo.c b/statinfo.c
index 5e00af127d..d9ddcf9382 100644
--- a/statinfo.c
+++ b/statinfo.c
@@ -72,13 +72,13 @@ int match_stat_data(const struct stat_data *sd, struct stat *st)
 	    sd->sd_ctime.sec != (unsigned int)st->st_ctime)
 		changed |= CTIME_CHANGED;
 
-#ifdef USE_NSEC
-	if (cfg->check_stat && sd->sd_mtime.nsec != ST_MTIME_NSEC(*st))
-		changed |= MTIME_CHANGED;
-	if (cfg->trust_ctime && cfg->check_stat &&
-	    sd->sd_ctime.nsec != ST_CTIME_NSEC(*st))
-		changed |= CTIME_CHANGED;
-#endif
+	if (cfg->use_nanosec) {
+		if (cfg->check_stat && sd->sd_mtime.nsec != ST_MTIME_NSEC(*st))
+			changed |= MTIME_CHANGED;
+		if (cfg->trust_ctime && cfg->check_stat &&
+		    sd->sd_ctime.nsec != ST_CTIME_NSEC(*st))
+			changed |= CTIME_CHANGED;
+	}
 
 	if (cfg->check_stat) {
 		if (sd->sd_uid != (unsigned int) st->st_uid ||