diff --git a/src/add-ons/kernel/file_systems/bfs/kernel_interface.cpp b/src/add-ons/kernel/file_systems/bfs/kernel_interface.cpp
index ff7f4df2fa..5ff5bfdf75 100644
--- a/src/add-ons/kernel/file_systems/bfs/kernel_interface.cpp
+++ b/src/add-ons/kernel/file_systems/bfs/kernel_interface.cpp
@@ -358,7 +358,7 @@ bfs_read_pages(fs_volume _fs, fs_vnode _node, fs_cookie _cookie, off_t pos,
 
 		bool bufferOverflow = status == B_BUFFER_OVERFLOW;
 
-		size_t bytes;
+		size_t bytes = bytesLeft;
 		status = read_file_io_vec_pages(volume->Device(), fileVecs,
 			fileVecCount, vecs, count, &vecIndex, &vecOffset, &bytes);
 		if (status != B_OK || !bufferOverflow)
@@ -404,7 +404,7 @@ bfs_write_pages(fs_volume _fs, fs_vnode _node, fs_cookie _cookie, off_t pos,
 
 		bool bufferOverflow = status == B_BUFFER_OVERFLOW;
 
-		size_t bytes;
+		size_t bytes = bytesLeft;
 		status = write_file_io_vec_pages(volume->Device(), fileVecs,
 			fileVecCount, vecs, count, &vecIndex, &vecOffset, &bytes);
 		if (status != B_OK || !bufferOverflow)
diff --git a/src/add-ons/kernel/file_systems/fat/file.c b/src/add-ons/kernel/file_systems/fat/file.c
index f2791633c0..dede087809 100644
--- a/src/add-ons/kernel/file_systems/fat/file.c
+++ b/src/add-ons/kernel/file_systems/fat/file.c
@@ -1505,7 +1505,7 @@ dosfs_read_pages(fs_volume _fs, fs_vnode _node, fs_cookie _cookie, off_t pos,
 		struct file_io_vec fileVecs[8];
 		uint32 fileVecCount = 8;
 		bool bufferOverflow;
-		size_t bytes;
+		size_t bytes = bytesLeft;
 
 		status = file_map_translate(node->file_map, pos, bytesLeft, fileVecs,
 			&fileVecCount);
@@ -1557,7 +1557,7 @@ dosfs_write_pages(fs_volume _fs, fs_vnode _node, fs_cookie _cookie, off_t pos,
 		struct file_io_vec fileVecs[8];
 		uint32 fileVecCount = 8;
 		bool bufferOverflow;
-		size_t bytes;
+		size_t bytes = bytesLeft;
 
 		status = file_map_translate(node->file_map, pos, bytesLeft, fileVecs,
 			&fileVecCount);