diff --git a/CHANGES b/CHANGES
index d57e5ef08e..b33425796c 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,7 @@
+4361.	[cleanup]	Where supported, file modification times returned
+			by isc_file_getmodtime() are now accurate to the
+			nanosecond. [RT #41968]
+
 4360.	[bug]		Silence spurious 'bad key type' message when there is
 			a existing TSIG key. [RT #42195]
 
diff --git a/configure b/configure
index b886de4e27..c7f362bce1 100755
--- a/configure
+++ b/configure
@@ -722,6 +722,7 @@ IRS_PLATFORM_USEDECLSPEC
 LWRES_PLATFORM_USEDECLSPEC
 ISC_PLATFORM_USEDECLSPEC
 ISC_PLATFORM_RLIMITTYPE
+ISC_PLATFORM_HAVESTATNSEC
 ISC_PLATFORM_HAVESYSUNH
 LWRES_PLATFORM_QUADFORMAT
 ISC_PLATFORM_QUADFORMAT
@@ -19096,6 +19097,34 @@ $as_echo "#define NEED_OPTARG 1" >>confdefs.h
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 
+#
+# Check for nanoseconds in file stats
+#
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking st_mtim.tv_nsec" >&5
+$as_echo_n "checking st_mtim.tv_nsec... " >&6; }
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <sys/fcntl.h>
+int
+main ()
+{
+struct stat s; return(s.st_mtim.tv_nsec);
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+        ISC_PLATFORM_HAVESTATNSEC="#define ISC_PLATFORM_HAVESTATNSEC 1"
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+        ISC_PLATFORM_HAVESTATNSEC="#undef ISC_PLATFORM_HAVESTATNSEC"
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+
+
 #
 # BSD/OS, and perhaps some others, don't define rlim_t.
 #
diff --git a/configure.in b/configure.in
index 2799501fc8..70e2097390 100644
--- a/configure.in
+++ b/configure.in
@@ -3485,6 +3485,17 @@ AC_TRY_COMPILE([
 GEN_NEED_OPTARG="-DNEED_OPTARG=1"
 AC_DEFINE(NEED_OPTARG, 1, [Defined if extern char *optarg is not declared.])])
 
+#
+# Check for nanoseconds in file stats
+#
+AC_MSG_CHECKING(st_mtim.tv_nsec)
+AC_TRY_COMPILE([#include <sys/fcntl.h>],[struct stat s; return(s.st_mtim.tv_nsec);],
+	[AC_MSG_RESULT(yes)
+        ISC_PLATFORM_HAVESTATNSEC="#define ISC_PLATFORM_HAVESTATNSEC 1"],
+	[AC_MSG_RESULT(no)
+        ISC_PLATFORM_HAVESTATNSEC="#undef ISC_PLATFORM_HAVESTATNSEC"])
+AC_SUBST(ISC_PLATFORM_HAVESTATNSEC)
+
 #
 # BSD/OS, and perhaps some others, don't define rlim_t.
 #
diff --git a/lib/isc/include/isc/platform.h.in b/lib/isc/include/isc/platform.h.in
index 2c6e2a51ac..99d08ba514 100644
--- a/lib/isc/include/isc/platform.h.in
+++ b/lib/isc/include/isc/platform.h.in
@@ -249,6 +249,11 @@
  */
 @ISC_PLATFORM_KRB5HEADER@
 
+/*
+ * Define if the system has nanosecond-level accuracy in file stats.
+ */
+@ISC_PLATFORM_HAVESTATNSEC@
+
 /*
  * Type used for resource limits.
  */
diff --git a/lib/isc/unix/file.c b/lib/isc/unix/file.c
index 1f51d001fa..1013cb5d86 100644
--- a/lib/isc/unix/file.c
+++ b/lib/isc/unix/file.c
@@ -149,11 +149,11 @@ isc_file_getmodtime(const char *file, isc_time_t *modtime) {
 	result = file_stats(file, &stats);
 
 	if (result == ISC_R_SUCCESS)
-		/*
-		 * XXXDCL some operating systems provide nanoseconds, too,
-		 * such as BSD/OS via st_mtimespec.
-		 */
+#ifdef ISC_PLATFORM_HAVESTATNSEC
+		isc_time_set(modtime, stats.st_mtime, stats.st_mtim.tv_nsec);
+#else
 		isc_time_set(modtime, stats.st_mtime, 0);
+#endif
 
 	return (result);
 }