diff --git a/src/common/filesystem/include/fs_files.h b/src/common/filesystem/include/fs_files.h
index ada77ca6e..7a2871a71 100644
--- a/src/common/filesystem/include/fs_files.h
+++ b/src/common/filesystem/include/fs_files.h
@@ -279,7 +279,7 @@ public:
 		if (len > 0)
 		{
 			Size length = mReader->Read(buffer.allocate(len), len);
-			if (length < len) buffer.allocate(length);
+			if ((size_t)length < len) buffer.allocate(length);
 		}
 		return buffer;
 	}
diff --git a/src/common/filesystem/source/file_zip.cpp b/src/common/filesystem/source/file_zip.cpp
index 352c7adc2..dfeb41ea8 100644
--- a/src/common/filesystem/source/file_zip.cpp
+++ b/src/common/filesystem/source/file_zip.cpp
@@ -52,7 +52,7 @@ namespace FileSys {
 //
 //==========================================================================
 
-static bool UncompressZipLump(char *Cache, FileReader &Reader, int Method, int LumpSize, int CompressedSize, int GPFlags, bool exceptions)
+static bool UncompressZipLump(char *Cache, FileReader &Reader, int Method, ptrdiff_t LumpSize, ptrdiff_t CompressedSize, int GPFlags, bool exceptions)
 {
 	switch (Method)
 	{
@@ -79,7 +79,7 @@ static bool UncompressZipLump(char *Cache, FileReader &Reader, int Method, int L
 	case METHOD_IMPLODE:
 	{
 		FZipExploder exploder;
-		if (exploder.Explode((unsigned char*)Cache, LumpSize, Reader, CompressedSize, GPFlags) == -1)
+		if (exploder.Explode((unsigned char*)Cache, (unsigned)LumpSize, Reader, (unsigned)CompressedSize, GPFlags) == -1)
 		{
 			// decompression failed so zero the cache.
 			memset(Cache, 0, LumpSize);
@@ -89,7 +89,7 @@ static bool UncompressZipLump(char *Cache, FileReader &Reader, int Method, int L
 
 	case METHOD_SHRINK:
 	{
-		ShrinkLoop((unsigned char *)Cache, LumpSize, Reader, CompressedSize);
+		ShrinkLoop((unsigned char *)Cache, (unsigned)LumpSize, Reader, (unsigned)CompressedSize);
 		break;
 	}
 
@@ -604,8 +604,8 @@ static int AppendToZip(FileWriter *zip_file, const FCompressedBuffer &content, s
 	local.ModDate = LittleShort(dostime.first);
 	local.ModTime = LittleShort(dostime.second);
 	local.CRC32 = content.mCRC32;
-	local.UncompressedSize = LittleLong(content.mSize);
-	local.CompressedSize = LittleLong(content.mCompressedSize);
+	local.UncompressedSize = LittleLong((unsigned)content.mSize);
+	local.CompressedSize = LittleLong((unsigned)content.mCompressedSize);
 	local.NameLength = LittleShort((unsigned short)strlen(content.filename));
 	local.ExtraLength = 0;
 
@@ -646,8 +646,8 @@ int AppendCentralDirectory(FileWriter *zip_file, const FCompressedBuffer &conten
 	dir.ModTime = LittleShort(dostime.first);
 	dir.ModDate = LittleShort(dostime.second);
 	dir.CRC32 = content.mCRC32;
-	dir.CompressedSize32 = LittleLong(content.mCompressedSize);
-	dir.UncompressedSize32 = LittleLong(content.mSize);
+	dir.CompressedSize32 = LittleLong((unsigned)content.mCompressedSize);
+	dir.UncompressedSize32 = LittleLong((unsigned)content.mSize);
 	dir.NameLength = LittleShort((unsigned short)strlen(content.filename));
 	dir.ExtraLength = 0;
 	dir.CommentLength = 0;
diff --git a/src/common/filesystem/source/files.cpp b/src/common/filesystem/source/files.cpp
index d17ca7002..7bf013060 100644
--- a/src/common/filesystem/source/files.cpp
+++ b/src/common/filesystem/source/files.cpp
@@ -323,7 +323,7 @@ char *MemoryReader::Gets(char *strbuf, ptrdiff_t len)
 	return strbuf;
 }
 
-int BufferingReader::FillBuffer(size_t newpos)
+int BufferingReader::FillBuffer(ptrdiff_t newpos)
 {
 	if (newpos > Length) newpos = Length;
 	if (newpos < bufferpos) return 0;
diff --git a/src/common/filesystem/source/files_internal.h b/src/common/filesystem/source/files_internal.h
index d5613b329..aa3595cbf 100644
--- a/src/common/filesystem/source/files_internal.h
+++ b/src/common/filesystem/source/files_internal.h
@@ -35,7 +35,7 @@ class BufferingReader : public MemoryReader
 	std::unique_ptr<FileReaderInterface> baseReader;
 	ptrdiff_t bufferpos = 0;
 
-	int FillBuffer(size_t newpos);
+	int FillBuffer(ptrdiff_t newpos);
 public:
 	BufferingReader(FileReaderInterface* base)
 		: baseReader(base)
diff --git a/src/common/filesystem/source/filesystem.cpp b/src/common/filesystem/source/filesystem.cpp
index 9f38ecd9f..e265f5cba 100644
--- a/src/common/filesystem/source/filesystem.cpp
+++ b/src/common/filesystem/source/filesystem.cpp
@@ -409,9 +409,9 @@ void FileSystem::AddFile (const char *filename, FileReader *filer, LumpFilterInf
 		uint32_t lumpstart = (uint32_t)FileInfo.size();
 
 		resfile->SetFirstLump(lumpstart);
-		for (uint32_t i=0; i < resfile->EntryCount(); i++)
+		for (int i = 0; i < resfile->EntryCount(); i++)
 		{
-			FResourceLump *lump = resfile->GetLump(i);
+			FResourceLump* lump = resfile->GetLump(i);
 			FileInfo.resize(FileInfo.size() + 1);
 			FileSystem::LumpRecord* lump_p = &FileInfo.back();
 			lump_p->SetFromLump((int)Files.size(), lump, stringpool);
@@ -419,7 +419,7 @@ void FileSystem::AddFile (const char *filename, FileReader *filer, LumpFilterInf
 
 		Files.push_back(resfile);
 
-		for (uint32_t i=0; i < resfile->EntryCount(); i++)
+		for (int i = 0; i < resfile->EntryCount(); i++)
 		{
 			int flags = resfile->GetEntryFlags(i);
 			if (flags & LUMPF_EMBEDDED)
@@ -454,7 +454,7 @@ void FileSystem::AddFile (const char *filename, FileReader *filer, LumpFilterInf
 			else
 				fprintf(hashfile, "file: %s, Directory structure\n", filename);
 
-			for (uint32_t i = 0; i < resfile->EntryCount(); i++)
+			for (int i = 0; i < resfile->EntryCount(); i++)
 			{
 				int flags = resfile->GetEntryFlags(i);
 				if (!(flags & LUMPF_EMBEDDED))