diff --git a/include/SDL3/SDL_filesystem.h b/include/SDL3/SDL_filesystem.h
index 17666a95d2a757..972e919e917d95 100644
--- a/include/SDL3/SDL_filesystem.h
+++ b/include/SDL3/SDL_filesystem.h
@@ -246,13 +246,14 @@ typedef enum SDL_StatPathType
     SDL_STATPATHTYPE_OTHER /**< something completely different like a device node (not a symlink, those are always followed) */
 } SDL_StatPathType;
 
+/* SDL timestamps are in _nanoseconds_ since the Unix epoch (Jan 1, 1970). */
 typedef struct SDL_Stat
 {
     SDL_StatPathType filetype;  /* is this a file? a dir? something else? */
-    Sint64 filesize;    /* size in bytes */
-    Sint64 modtime;     /* SDL filesystem timestamp */
-    Sint64 createtime;  /* SDL filesystem timestamp */
-    Sint64 accesstime;  /* SDL filesystem timestamp */
+    Uint64 filesize;    /* size in bytes */
+    Uint64 modtime;     /* SDL filesystem timestamp */
+    Uint64 createtime;  /* SDL filesystem timestamp */
+    Uint64 accesstime;  /* SDL filesystem timestamp */
 } SDL_Stat;
 
 
@@ -349,10 +350,10 @@ extern DECLSPEC void SDLCALL SDL_DestroyFilesystem(SDL_FSops *fs);
 extern DECLSPEC const char * SDLCALL SDL_GetFilePathSeparator(void);
 
 /* converts an SDL file timestamp into a win32 FILETIME (100-nanosecond intervals since January 1, 1601). Fills in the two 32-bit values of the win32 struct. */
-extern DECLSPEC void SDLCALL SDL_FileTimeToWindows(Sint64 ftime, Uint32 *low, Uint32 *high);
+extern DECLSPEC void SDLCALL SDL_FileTimeToWindows(Uint64 ftime, Uint32 *low, Uint32 *high);
 
 /* converts an SDL file timestamp into a Unix time_t (seconds since the Unix epoch). */
-extern DECLSPEC Sint64 SDLCALL SDL_FileTimeToUnix(Sint64 ftime);
+extern DECLSPEC Uint64 SDLCALL SDL_FileTimeToUnix(Uint64 ftime);
 
 
 /* Ends C function definitions when using C++ */
diff --git a/src/dynapi/SDL_dynapi_procs.h b/src/dynapi/SDL_dynapi_procs.h
index 325066fdd9d241..3d2e9f83ba7fa7 100644
--- a/src/dynapi/SDL_dynapi_procs.h
+++ b/src/dynapi/SDL_dynapi_procs.h
@@ -1030,5 +1030,5 @@ SDL_DYNAPI_PROC(int,SDL_FSstat,(SDL_FSops *a, const char *b, SDL_Stat *c),(a,b,c
 SDL_DYNAPI_PROC(SDL_PropertiesID,SDL_GetFSProperties,(SDL_FSops *a),(a),return)
 SDL_DYNAPI_PROC(void,SDL_DestroyFilesystem,(SDL_FSops *a),(a),)
 SDL_DYNAPI_PROC(const char*,SDL_GetFilePathSeparator,(void),(),return)
-SDL_DYNAPI_PROC(void,SDL_FileTimeToWindows,(Sint64 a, Uint32 *b, Uint32 *c),(a,b,c),)
-SDL_DYNAPI_PROC(Sint64,SDL_FileTimeToUnix,(Sint64 a),(a),return)
+SDL_DYNAPI_PROC(void,SDL_FileTimeToWindows,(Uint64 a, Uint32 *b, Uint32 *c),(a,b,c),)
+SDL_DYNAPI_PROC(Uint64,SDL_FileTimeToUnix,(Uint64 a),(a),return)
diff --git a/src/filesystem/SDL_filesystem.c b/src/filesystem/SDL_filesystem.c
index 5ac4c2c13eeab0..874b925e766ed5 100644
--- a/src/filesystem/SDL_filesystem.c
+++ b/src/filesystem/SDL_filesystem.c
@@ -108,21 +108,22 @@ const char *SDL_GetFilePathSeparator(void)
     return PLATFORM_PATH_SEPARATOR;
 }
 
-void SDL_FileTimeToWindows(Sint64 ftime, Uint32 *low, Uint32 *high)
+void SDL_FileTimeToWindows(Uint64 ftime, Uint32 *low, Uint32 *high)
 {
-    const Uint64 delta_1601_epoch_s = 11644473600; // [seconds] (seconds between 1/1/1601 and 1/1/1970)
-    const Uint64 cvt = (delta_1601_epoch_s + ftime) * 10000000ull; // [100ns]
+    const Uint64 delta_1601_epoch_ns = 11644473600ull * SDL_NS_PER_SECOND; // [ns] (nanoseconds between 1/1/1601 and 1/1/1970, 11644473600 seconds * 1000000000)
+    const Uint64 cvt = (ftime + delta_1601_epoch_ns) / 100ull; // [100ns] (adjust to epoch and convert nanoseconds to 1/100th nanosecond units).
     if (low) {
-        *low = cvt & 0xFFFFFFFFull;
+        *low = (Uint32) cvt;
     }
     if (high) {
-        *high = cvt >> 32;
+        *high = (Uint32) (cvt >> 32);
     }
 }
 
-Sint64 SDL_FileTimeToUnix(Sint64 ftime)
+Uint64 SDL_FileTimeToUnix(Uint64 ftime)
 {
-    return ftime;  // currently SDL time is just the unix epoch.
+    // SDL time uses the unix epoch, but in nanoseconds. Divide to convert to seconds.
+    return ftime / SDL_NS_PER_SECOND;
 }
 
 
diff --git a/src/filesystem/posix/SDL_sysfsops.c b/src/filesystem/posix/SDL_sysfsops.c
index a1412f33d08b26..a48f1456ec89b6 100644
--- a/src/filesystem/posix/SDL_sysfsops.c
+++ b/src/filesystem/posix/SDL_sysfsops.c
@@ -79,18 +79,19 @@ int SDL_SYS_FSstat(SDL_FSops *fs, const char *fullpath, SDL_Stat *st)
         return SDL_SetError("Can't stat: %s", strerror(errno));
     } else if (S_ISREG(statbuf.st_mode)) {
         st->filetype = SDL_STATPATHTYPE_FILE;
-        st->filesize = statbuf.st_size;
+        st->filesize = (Uint64) statbuf.st_size;
     } else if(S_ISDIR(statbuf.st_mode)) {
         st->filetype = SDL_STATPATHTYPE_DIRECTORY;
         st->filesize = 0;
     } else {
         st->filetype = SDL_STATPATHTYPE_OTHER;
-        st->filesize = statbuf.st_size;
+        st->filesize = (Uint64) statbuf.st_size;
     }
 
-    st->modtime = statbuf.st_mtime;
-    st->createtime = statbuf.st_ctime;
-    st->accesstime = statbuf.st_atime;
+    // SDL file time is nanoseconds since the Unix epoch, so we just need to convert secs -> nanosecs.
+    st->modtime = ((Uint64) statbuf.st_mtime) * SDL_NS_PER_SECOND;
+    st->createtime = ((Uint64) statbuf.st_ctime) * SDL_NS_PER_SECOND;
+    st->accesstime = ((Uint64) statbuf.st_atime) * SDL_NS_PER_SECOND;
 
     return 0;
 }
diff --git a/src/filesystem/windows/SDL_sysfsops.c b/src/filesystem/windows/SDL_sysfsops.c
index 96ab93cbf732ac..a8fab983b24e93 100644
--- a/src/filesystem/windows/SDL_sysfsops.c
+++ b/src/filesystem/windows/SDL_sysfsops.c
@@ -117,17 +117,16 @@ int SDL_SYS_FSmkdir(SDL_FSops *fs, const char *fullpath)
     return !rc ? WIN_SetError("Couldn't create directory") : 0;
 }
 
-static Sint64 FileTimeToSDLTime(const FILETIME *ft)
+static Uint64 FileTimeToSDLTime(const FILETIME *ft)
 {
-    const ULONGLONG nanosecToMillisec = 10000000ull;
-    const ULONGLONG delta_1601_epoch_s = 11644473600ull; // [seconds] (seconds between 1/1/1601 and 1/1/1970)
+    const Uint64 delta_1601_epoch_100ns = 11644473600ull * 10000000ull; // [ns] (100-ns chunks between 1/1/1601 and 1/1/1970, 11644473600 seconds * 10000000)
     ULARGE_INTEGER large;
     large.LowPart = ft->dwLowDateTime;
     large.HighPart = ft->dwHighDateTime;
     if (large.QuadPart == 0) {
         return 0;  // unsupported on this filesystem...0 is fine, I guess.
     }
-    return (Sint64) ((large.QuadPart - delta_1601_epoch_s) / nanosecToMillisec);
+    return (((Uint64)large.QuadPart) - delta_1601_epoch_100ns) * 100;  // [ns] (adjust to epoch and convert 1/100th nanosecond units to nanoseconds).
 }
 
 int SDL_SYS_FSstat(SDL_FSops *fs, const char *fullpath, SDL_Stat *st)
@@ -153,10 +152,10 @@ int SDL_SYS_FSstat(SDL_FSops *fs, const char *fullpath, SDL_Stat *st)
         st->filesize = 0;
     } else if (winstat.dwFileAttributes & (FILE_ATTRIBUTE_OFFLINE | FILE_ATTRIBUTE_DEVICE)) {
         st->filetype = SDL_STATPATHTYPE_OTHER;
-        st->filesize = (Sint64) ((((Uint64) winstat.nFileSizeHigh) << 32) | winstat.nFileSizeLow);
+        st->filesize = ((((Uint64) winstat.nFileSizeHigh) << 32) | winstat.nFileSizeLow);
     } else {
         st->filetype = SDL_STATPATHTYPE_FILE;
-        st->filesize = (Sint64) ((((Uint64) winstat.nFileSizeHigh) << 32) | winstat.nFileSizeLow);
+        st->filesize = ((((Uint64) winstat.nFileSizeHigh) << 32) | winstat.nFileSizeLow);
     }
 
     return 1;
diff --git a/test/testfilesystem.c b/test/testfilesystem.c
index bd15ee6161a28c..36bb81bc1b5cbb 100644
--- a/test/testfilesystem.c
+++ b/test/testfilesystem.c
@@ -38,7 +38,7 @@ static int SDLCALL enum_callback(void *userdata, SDL_FSops *fsops, const char *o
         } else {
             type = "OTHER";
         }
-        SDL_Log("%s (type=%s, size=%" SDL_PRIs64 ", mod=%" SDL_PRIs64 ", create=%" SDL_PRIs64 ", access=%" SDL_PRIs64 ")",
+        SDL_Log("%s (type=%s, size=%" SDL_PRIu64 ", mod=%" SDL_PRIu64 ", create=%" SDL_PRIu64 ", access=%" SDL_PRIu64 ")",
                 fullpath, type, statbuf.filesize, statbuf.modtime, statbuf.createtime, statbuf.accesstime);
 
         if (statbuf.filetype == SDL_STATPATHTYPE_DIRECTORY) {