diff --git a/src/gba/gba-savedata.c b/src/gba/gba-savedata.c
index 83b0cb834..d1f39441f 100644
--- a/src/gba/gba-savedata.c
+++ b/src/gba/gba-savedata.c
@@ -142,7 +142,7 @@ void GBASavedataInitFlash(struct GBASavedata* savedata) {
 		end = 0;
 		savedata->data = anonymousMemoryMap(SIZE_CART_FLASH1M);
 	} else {
-		end = savedata->vf->seek(savedata->vf, 0, SEEK_END);
+		end = savedata->vf->size(savedata->vf);
 		if (end < SIZE_CART_FLASH512) {
 			savedata->vf->truncate(savedata->vf, SIZE_CART_FLASH1M);
 			flashSize = SIZE_CART_FLASH1M;
@@ -168,7 +168,7 @@ void GBASavedataInitEEPROM(struct GBASavedata* savedata) {
 		end = 0;
 		savedata->data = anonymousMemoryMap(SIZE_CART_EEPROM);
 	} else {
-		end = savedata->vf->seek(savedata->vf, 0, SEEK_END);
+		end = savedata->vf->size(savedata->vf);
 		if (end < SIZE_CART_EEPROM) {
 			savedata->vf->truncate(savedata->vf, SIZE_CART_EEPROM);
 		}
@@ -191,7 +191,7 @@ void GBASavedataInitSRAM(struct GBASavedata* savedata) {
 		end = 0;
 		savedata->data = anonymousMemoryMap(SIZE_CART_SRAM);
 	} else {
-		end = savedata->vf->seek(savedata->vf, 0, SEEK_END);
+		end = savedata->vf->size(savedata->vf);
 		if (end < SIZE_CART_SRAM) {
 			savedata->vf->truncate(savedata->vf, SIZE_CART_SRAM);
 		}
diff --git a/src/gba/gba.c b/src/gba/gba.c
index 922c84f3a..2fec3604a 100644
--- a/src/gba/gba.c
+++ b/src/gba/gba.c
@@ -445,7 +445,7 @@ void GBADetachDebugger(struct GBA* gba) {
 
 void GBALoadROM(struct GBA* gba, struct VFile* vf, struct VFile* sav, const char* fname) {
 	gba->romVf = vf;
-	gba->pristineRomSize = vf->seek(vf, 0, SEEK_END);
+	gba->pristineRomSize = vf->size(vf);
 	vf->seek(vf, 0, SEEK_SET);
 	if (gba->pristineRomSize > SIZE_CART0) {
 		gba->pristineRomSize = SIZE_CART0;
diff --git a/src/platform/qt/VFileDevice.cpp b/src/platform/qt/VFileDevice.cpp
index bf3e41982..62597a50b 100644
--- a/src/platform/qt/VFileDevice.cpp
+++ b/src/platform/qt/VFileDevice.cpp
@@ -27,9 +27,5 @@ qint64 VFileDevice::writeData(const char* data, qint64 maxSize) {
 }
 
 qint64 VFileDevice::size() const {
-	// TODO: Add size method to VFile so this can be actually const
-	ssize_t pos = m_vf->seek(m_vf, 0, SEEK_CUR);
-	qint64 size = m_vf->seek(m_vf, 0, SEEK_END);
-	m_vf->seek(m_vf, pos, SEEK_SET);
-	return size;
+	return m_vf->size(m_vf);
 }
diff --git a/src/util/patch-ups.c b/src/util/patch-ups.c
index 33f71cee2..f7fa1c4e6 100644
--- a/src/util/patch-ups.c
+++ b/src/util/patch-ups.c
@@ -31,7 +31,7 @@ bool loadPatchUPS(struct Patch* patch) {
 		return false;
 	}
 
-	size_t filesize = patch->vf->seek(patch->vf, 0, SEEK_END);
+	size_t filesize = patch->vf->size(patch->vf);
 
 	uint32_t goodCrc32;
 	patch->vf->seek(patch->vf, PATCH_CHECKSUM, SEEK_END);
@@ -61,7 +61,7 @@ size_t _UPSOutputSize(struct Patch* patch, size_t inSize) {
 bool _UPSApplyPatch(struct Patch* patch, void* out, size_t outSize) {
 	// TODO: Input checksum
 
-	size_t filesize = patch->vf->seek(patch->vf, 0, SEEK_END);
+	size_t filesize = patch->vf->size(patch->vf);
 	patch->vf->seek(patch->vf, 4, SEEK_SET);
 	_UPSDecodeLength(patch->vf); // Discard input size
 	if (_UPSDecodeLength(patch->vf) != outSize) {
diff --git a/src/util/vfs.c b/src/util/vfs.c
index b50f610ad..55e7ec874 100644
--- a/src/util/vfs.c
+++ b/src/util/vfs.c
@@ -9,6 +9,7 @@
 
 #include <fcntl.h>
 #include <dirent.h>
+#include <sys/stat.h>
 
 #ifndef _WIN32
 #include <sys/mman.h>
@@ -35,6 +36,7 @@ static ssize_t _vfdWrite(struct VFile* vf, const void* buffer, size_t size);
 static void* _vfdMap(struct VFile* vf, size_t size, int flags);
 static void _vfdUnmap(struct VFile* vf, void* memory, size_t size);
 static void _vfdTruncate(struct VFile* vf, size_t size);
+static ssize_t _vfdSize(struct VFile* vf);
 
 static bool _vdClose(struct VDir* vd);
 static void _vdRewind(struct VDir* vd);
@@ -73,6 +75,7 @@ struct VFile* VFileFromFD(int fd) {
 	vfd->d.map = _vfdMap;
 	vfd->d.unmap = _vfdUnmap;
 	vfd->d.truncate = _vfdTruncate;
+	vfd->d.size = _vfdSize;
 
 	return &vfd->d;
 }
@@ -137,9 +140,12 @@ static void* _vfdMap(struct VFile* vf, size_t size, int flags) {
 		createFlags = PAGE_READWRITE;
 		mapFiles = FILE_MAP_WRITE;
 	}
-	size_t location = lseek(vfd->fd, 0, SEEK_CUR);
-	size_t fileSize = lseek(vfd->fd, 0, SEEK_END);
-	lseek(vfd->fd, location, SEEK_SET);
+	size_t fileSize;
+	struct stat stat;
+	if (fstat(vfd->fd, &stat) < 0) {
+		return 0;
+	}
+	fileSize = stat.st_size;
 	if (size > fileSize) {
 		size = fileSize;
 	}
@@ -161,6 +167,15 @@ static void _vfdTruncate(struct VFile* vf, size_t size) {
 	ftruncate(vfd->fd, size);
 }
 
+static ssize_t _vfdSize(struct VFile* vf) {
+	struct VFileFD* vfd = (struct VFileFD*) vf;
+	struct stat stat;
+	if (fstat(vfd->fd, &stat) < 0) {
+		return -1;
+	}
+	return stat.st_size;
+}
+
 struct VDirEntryDE {
 	struct VDirEntry d;
 	struct dirent* ent;
diff --git a/src/util/vfs.h b/src/util/vfs.h
index 1ce7798fb..3394317c7 100644
--- a/src/util/vfs.h
+++ b/src/util/vfs.h
@@ -22,6 +22,7 @@ struct VFile {
 	void* (*map)(struct VFile* vf, size_t size, int flags);
 	void (*unmap)(struct VFile* vf, void* memory, size_t size);
 	void (*truncate)(struct VFile* vf, size_t size);
+	ssize_t (*size)(struct VFile* vf);
 };
 
 struct VDirEntry {
diff --git a/src/util/vfs/vfs-zip.c b/src/util/vfs/vfs-zip.c
index 182cfe256..02e6216fe 100644
--- a/src/util/vfs/vfs-zip.c
+++ b/src/util/vfs/vfs-zip.c
@@ -43,6 +43,7 @@ static ssize_t _vfzWrite(struct VFile* vf, const void* buffer, size_t size);
 static void* _vfzMap(struct VFile* vf, size_t size, int flags);
 static void _vfzUnmap(struct VFile* vf, void* memory, size_t size);
 static void _vfzTruncate(struct VFile* vf, size_t size);
+static ssize_t _vfzSize(struct VFile* vf);
 
 static bool _vdzClose(struct VDir* vd);
 static void _vdzRewind(struct VDir* vd);
@@ -229,6 +230,11 @@ void _vfzTruncate(struct VFile* vf, size_t size) {
 	UNUSED(size);
 }
 
+ssize_t _vfzSize(struct VFile* vf) {
+	struct VFileZip* vfz = (struct VFileZip*) vf;
+	return vfz->fileSize;
+}
+
 bool _vdzClose(struct VDir* vd) {
 	struct VDirZip* vdz = (struct VDirZip*) vd;
 	if (zip_close(vdz->z) < 0) {
@@ -295,6 +301,7 @@ struct VFile* _vdzOpenFile(struct VDir* vd, const char* path, int mode) {
 	vfz->d.map = _vfzMap;
 	vfz->d.unmap = _vfzUnmap;
 	vfz->d.truncate = _vfzTruncate;
+	vfz->d.size = _vfzSize;
 
 	return &vfz->d;
 }