diff --git a/Core/Dialog/SavedataParam.cpp b/Core/Dialog/SavedataParam.cpp
index 88a6fceaff..648c73d988 100644
--- a/Core/Dialog/SavedataParam.cpp
+++ b/Core/Dialog/SavedataParam.cpp
@@ -92,7 +92,7 @@ namespace
 		size_t result = pspFileSystem.WriteFile(handle, data, dataSize);
 		pspFileSystem.CloseFile(handle);
 
-		return result != 0;
+		return result == dataSize;
 	}
 
 	bool PSPMatch(std::string text, std::string regexp)
diff --git a/Core/FileSystems/DirectoryFileSystem.cpp b/Core/FileSystems/DirectoryFileSystem.cpp
index d77616a83e..499eed79c5 100644
--- a/Core/FileSystems/DirectoryFileSystem.cpp
+++ b/Core/FileSystems/DirectoryFileSystem.cpp
@@ -290,10 +290,19 @@ size_t DirectoryFileHandle::Read(u8* pointer, s64 size)
 size_t DirectoryFileHandle::Write(const u8* pointer, s64 size)
 {
 	size_t bytesWritten = 0;
+	bool diskFull = false;
+
 #ifdef _WIN32
-	::WriteFile(hFile, (LPVOID)pointer, (DWORD)size, (LPDWORD)&bytesWritten, 0);
+	BOOL success = ::WriteFile(hFile, (LPVOID)pointer, (DWORD)size, (LPDWORD)&bytesWritten, 0);
+	if (success == FALSE) {
+		DWORD err = GetLastError();
+		diskFull = err == ERROR_DISK_FULL || err == ERROR_NOT_ENOUGH_QUOTA;
+	}
 #else
 	bytesWritten = write(hFile, pointer, size);
+	if (bytesWritten == (size_t)-1) {
+		diskFull = errno == ENOSPC;
+	}
 #endif
 	if (needsTrunc_ != -1) {
 		off_t off = (off_t)Seek(0, FILEMOVE_CURRENT);
@@ -301,6 +310,13 @@ size_t DirectoryFileHandle::Write(const u8* pointer, s64 size)
 			needsTrunc_ = off;
 		}
 	}
+
+	if (diskFull) {
+		// Sign extend on 64-bit.
+		ERROR_LOG(FILESYS, "Disk full");
+		return (size_t)(s64)(s32)SCE_KERNEL_ERROR_ERRNO_DEVICE_NO_FREE_SPACE;
+	}
+
 	return bytesWritten;
 }
 
diff --git a/Core/HW/AsyncIOManager.cpp b/Core/HW/AsyncIOManager.cpp
index 89dfaf6481..c022f16404 100644
--- a/Core/HW/AsyncIOManager.cpp
+++ b/Core/HW/AsyncIOManager.cpp
@@ -96,7 +96,8 @@ void AsyncIOManager::Read(u32 handle, u8 *buf, size_t bytes) {
 }
 
 void AsyncIOManager::Write(u32 handle, u8 *buf, size_t bytes) {
-	size_t result = pspFileSystem.WriteFile(handle, buf, bytes);
+	// We want to sign extend this on 32-bit.
+	AsyncIOResult result = (ssize_t)pspFileSystem.WriteFile(handle, buf, bytes);
 	EventResult(handle, result);
 }
 
diff --git a/Core/HW/AsyncIOManager.h b/Core/HW/AsyncIOManager.h
index 8fb96a16ee..76d6f5e7f9 100644
--- a/Core/HW/AsyncIOManager.h
+++ b/Core/HW/AsyncIOManager.h
@@ -44,7 +44,7 @@ struct AsyncIOEvent {
 };
 
 // TODO: Something better.
-typedef size_t AsyncIOResult;
+typedef s64 AsyncIOResult;
 
 typedef ThreadEventQueue<NoBase, AsyncIOEvent, AsyncIOEventType, IO_EVENT_INVALID, IO_EVENT_SYNC, IO_EVENT_FINISH> IOThreadEventQueue;
 class AsyncIOManager : public IOThreadEventQueue {
diff --git a/UI/BackgroundAudio.cpp b/UI/BackgroundAudio.cpp
index 8abe4ac9b1..5116b2c7b9 100644
--- a/UI/BackgroundAudio.cpp
+++ b/UI/BackgroundAudio.cpp
@@ -57,7 +57,7 @@ public:
 				Nothing = temp >> 16;
 
 				if (codec == PSP_CODEC_AT3) {
-					// The first two bytes are actually not useful part of the extradata.
+					// The first two bytes are actually not a useful part of the extradata.
 					// We already read 16 bytes, so make sure there's enough left.
 					if (file_.getCurrentChunkSize() >= 32) {
 						file_.readData(at3_extradata, 16);