diff --git a/headers/private/kernel/vfs.h b/headers/private/kernel/vfs.h
index 30392ed14c..5f1da653a8 100644
--- a/headers/private/kernel/vfs.h
+++ b/headers/private/kernel/vfs.h
@@ -302,10 +302,10 @@ public:
 									bool partialTransfer,
 									generic_size_t bytesTransferred) = 0;
 
-	static	status_t 			IORequestCallback(void* data,
+	static	void	 			IORequestCallback(void* data,
 									io_request* request, status_t status,
 									bool partialTransfer,
-									generic_size_t transferEndOffset);
+									generic_size_t bytesTransferred);
 };
 
 
diff --git a/src/system/kernel/cache/file_cache.cpp b/src/system/kernel/cache/file_cache.cpp
index 49b6dee5b7..5ef0929165 100644
--- a/src/system/kernel/cache/file_cache.cpp
+++ b/src/system/kernel/cache/file_cache.cpp
@@ -195,7 +195,7 @@ PrecacheIO::IOFinished(status_t status, bool partialTransfer,
 	phys_size_t pagesTransferred
 		= (bytesTransferred + B_PAGE_SIZE - 1) / B_PAGE_SIZE;
 
-	if (fOffset + (off_t)bytesTransferred > fCache->virtual_end)
+	if ((fOffset + (off_t)bytesTransferred) > fCache->virtual_end)
 		bytesTransferred = fCache->virtual_end - fOffset;
 
 	for (uint32 i = 0; i < pagesTransferred; i++) {
diff --git a/src/system/kernel/device_manager/IORequest.cpp b/src/system/kernel/device_manager/IORequest.cpp
index 0ed0aaae54..48b2e10d33 100644
--- a/src/system/kernel/device_manager/IORequest.cpp
+++ b/src/system/kernel/device_manager/IORequest.cpp
@@ -965,6 +965,7 @@ IORequest::NotifyFinished()
 	ASSERT(fPendingChildren == 0);
 	ASSERT(fChildren.IsEmpty()
 		|| dynamic_cast<IOOperation*>(fChildren.Head()) == NULL);
+	ASSERT(fTransferSize <= fLength);
 
 	// unlock the memory
 	if (fBuffer->IsMemoryLocked())
@@ -977,8 +978,9 @@ IORequest::NotifyFinished()
 	io_request_finished_callback finishedCallback = fFinishedCallback;
 	void* finishedCookie = fFinishedCookie;
 	status_t status = fStatus;
+	generic_size_t transferredBytes = fTransferSize;
 	generic_size_t lastTransferredOffset
-		= fRelativeParentOffset + fTransferSize;
+		= fRelativeParentOffset + transferredBytes;
 	bool partialTransfer = status != B_OK || fPartialTransfer;
 	bool deleteRequest = (fFlags & B_DELETE_IO_REQUEST) != 0;
 
@@ -991,7 +993,7 @@ IORequest::NotifyFinished()
 	// notify callback
 	if (finishedCallback != NULL) {
 		finishedCallback(finishedCookie, this, status, partialTransfer,
-			lastTransferredOffset);
+			transferredBytes);
 	}
 
 	// notify parent
@@ -1076,8 +1078,8 @@ void
 IORequest::SubRequestFinished(IORequest* request, status_t status,
 	bool partialTransfer, generic_size_t transferEndOffset)
 {
-	TRACE("IORequest::SubrequestFinished(%p, %#" B_PRIx32 ", %d, %"
-		B_PRIuGENADDR "): request: %p\n", request, status, partialTransfer, transferEndOffset, this);
+	TRACE("IORequest::SubrequestFinished(%p, %#" B_PRIx32 ", %d, %" B_PRIuGENADDR
+		"): request: %p\n", request, status, partialTransfer, transferEndOffset, this);
 
 	MutexLocker locker(fLock);
 
@@ -1122,8 +1124,6 @@ IORequest::SetTransferredBytes(bool partialTransfer,
 
 	MutexLocker _(fLock);
 
-	ASSERT(transferredBytes <= fLength);
-
 	fPartialTransfer = partialTransfer;
 	fTransferSize = transferredBytes;
 }
diff --git a/src/system/kernel/device_manager/IORequest.h b/src/system/kernel/device_manager/IORequest.h
index 8b262967e9..3d113a23de 100644
--- a/src/system/kernel/device_manager/IORequest.h
+++ b/src/system/kernel/device_manager/IORequest.h
@@ -199,10 +199,9 @@ typedef IOOperation io_operation;
 typedef DoublyLinkedList<IOOperation> IOOperationList;
 
 typedef struct IORequest io_request;
-typedef status_t (*io_request_finished_callback)(void* data,
+typedef void (*io_request_finished_callback)(void* data,
 			io_request* request, status_t status, bool partialTransfer,
-			generic_size_t transferEndOffset);
-			// TODO: Return type: status_t -> void
+			generic_size_t transferredBytes);
 typedef status_t (*io_request_iterate_callback)(void* data,
 			io_request* request, bool* _partialTransfer);
 
diff --git a/src/system/kernel/fs/vfs_request_io.cpp b/src/system/kernel/fs/vfs_request_io.cpp
index c8335244f6..57214cc41c 100644
--- a/src/system/kernel/fs/vfs_request_io.cpp
+++ b/src/system/kernel/fs/vfs_request_io.cpp
@@ -26,13 +26,12 @@ AsyncIOCallback::~AsyncIOCallback()
 }
 
 
-/* static */ status_t
+/* static */ void
 AsyncIOCallback::IORequestCallback(void* data, io_request* request,
-	status_t status, bool partialTransfer, generic_size_t transferEndOffset)
+	status_t status, bool partialTransfer, generic_size_t bytesTransferred)
 {
 	((AsyncIOCallback*)data)->IOFinished(status, partialTransfer,
-		transferEndOffset);
-	return B_OK;
+		bytesTransferred);
 }
 
 
@@ -257,27 +256,25 @@ do_iterative_fd_io_iterate(void* _cookie, io_request* request,
 }
 
 
-static status_t
+static void
 do_iterative_fd_io_finish(void* _cookie, io_request* request, status_t status,
-	bool partialTransfer, generic_size_t transferEndOffset)
+	bool partialTransfer, generic_size_t bytesTransferred)
 {
 	iterative_io_cookie* cookie = (iterative_io_cookie*)_cookie;
 
 	if (cookie->finished != NULL) {
 		cookie->finished(cookie->cookie, request, status, partialTransfer,
-			transferEndOffset);
+			bytesTransferred);
 	}
 
 	put_fd(cookie->descriptor);
 
 	if (cookie->next_finished_callback != NULL) {
 		cookie->next_finished_callback(cookie->next_finished_cookie, request,
-			status, partialTransfer, transferEndOffset);
+			status, partialTransfer, bytesTransferred);
 	}
 
 	delete cookie;
-
-	return B_OK;
 }
 
 
diff --git a/src/system/kernel/vm/VMAnonymousCache.cpp b/src/system/kernel/vm/VMAnonymousCache.cpp
index 6f94fcfc9f..04bae4bbfe 100644
--- a/src/system/kernel/vm/VMAnonymousCache.cpp
+++ b/src/system/kernel/vm/VMAnonymousCache.cpp
@@ -429,7 +429,6 @@ public:
 		}
 
 		fNextCallback->IOFinished(status, partialTransfer, bytesTransferred);
-
 		delete this;
 	}
 
diff --git a/src/system/kernel/vm/vm_page.cpp b/src/system/kernel/vm/vm_page.cpp
index 3b43b16083..ee4b956bac 100644
--- a/src/system/kernel/vm/vm_page.cpp
+++ b/src/system/kernel/vm/vm_page.cpp
@@ -1966,6 +1966,7 @@ public:
 
 	virtual void IOFinished(status_t status, bool partialTransfer,
 		generic_size_t bytesTransferred);
+
 private:
 	PageWriterRun*		fRun;
 	struct VMCache*		fCache;