diff --git a/CMakeLists.txt b/CMakeLists.txt
index 574018350..3341c804a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -2276,6 +2276,7 @@ if(GTEST_FOUND OR DOWNLOAD_GTEST)
     bezier.cpp
     blocklist_driver.cpp
     color.cpp
+    compression.cpp
     csv.cpp
     datafile.cpp
     fs.cpp
diff --git a/src/engine/shared/compression.cpp b/src/engine/shared/compression.cpp
index 35e6b3052..b04a234af 100644
--- a/src/engine/shared/compression.cpp
+++ b/src/engine/shared/compression.cpp
@@ -8,17 +8,17 @@
 unsigned char *CVariableInt::Pack(unsigned char *pDst, int i)
 {
 	*pDst = (i >> 25) & 0x40; // set sign bit if i<0
-	i = i ^ (i >> 31); // if(i<0) i = ~i
+	i ^= i >> 31; // if(i<0) i = ~i
 
 	*pDst |= i & 0x3F; // pack 6bit into dst
 	i >>= 6; // discard 6 bits
 	if(i)
 	{
 		*pDst |= 0x80; // set extend bit
-		while(1)
+		while(true)
 		{
 			pDst++;
-			*pDst = i & (0x7F); // pack 7bit
+			*pDst = i & 0x7F; // pack 7bit
 			i >>= 7; // discard 7 bits
 			*pDst |= (i != 0) << 7; // set extend bit (may branch)
 			if(!i)
@@ -32,7 +32,7 @@ unsigned char *CVariableInt::Pack(unsigned char *pDst, int i)
 
 const unsigned char *CVariableInt::Unpack(const unsigned char *pSrc, int *pInOut)
 {
-	int Sign = (*pSrc >> 6) & 1;
+	const int Sign = (*pSrc >> 6) & 1;
 	*pInOut = *pSrc & 0x3F;
 
 	do
@@ -40,35 +40,37 @@ const unsigned char *CVariableInt::Unpack(const unsigned char *pSrc, int *pInOut
 		if(!(*pSrc & 0x80))
 			break;
 		pSrc++;
-		*pInOut |= (*pSrc & (0x7F)) << (6);
+		*pInOut |= (*pSrc & 0x7F) << 6;
 
 		if(!(*pSrc & 0x80))
 			break;
 		pSrc++;
-		*pInOut |= (*pSrc & (0x7F)) << (6 + 7);
+		*pInOut |= (*pSrc & 0x7F) << (6 + 7);
 
 		if(!(*pSrc & 0x80))
 			break;
 		pSrc++;
-		*pInOut |= (*pSrc & (0x7F)) << (6 + 7 + 7);
+		*pInOut |= (*pSrc & 0x7F) << (6 + 7 + 7);
 
 		if(!(*pSrc & 0x80))
 			break;
 		pSrc++;
-		*pInOut |= (*pSrc & (0x1F)) << (6 + 7 + 7 + 7);
-	} while(0);
+		*pInOut |= (*pSrc & 0x0F) << (6 + 7 + 7 + 7);
+	} while(false);
 
 	pSrc++;
 	*pInOut ^= -Sign; // if(sign) *i = ~(*i)
 	return pSrc;
 }
 
-long CVariableInt::Decompress(const void *pSrc_, int Size, void *pDst_, int DstSize)
+long CVariableInt::Decompress(const void *pSrc_, int SrcSize, void *pDst_, int DstSize)
 {
+	dbg_assert(DstSize % sizeof(int) == 0, "invalid bounds");
+
 	const unsigned char *pSrc = (unsigned char *)pSrc_;
-	const unsigned char *pEnd = pSrc + Size;
+	const unsigned char *pEnd = pSrc + SrcSize;
 	int *pDst = (int *)pDst_;
-	int *pDstEnd = pDst + DstSize / 4;
+	const int *pDstEnd = pDst + DstSize / sizeof(int);
 	while(pSrc < pEnd)
 	{
 		if(pDst >= pDstEnd)
@@ -76,22 +78,24 @@ long CVariableInt::Decompress(const void *pSrc_, int Size, void *pDst_, int DstS
 		pSrc = CVariableInt::Unpack(pSrc, pDst);
 		pDst++;
 	}
-	return (unsigned char *)pDst - (unsigned char *)pDst_;
+	return (long)((unsigned char *)pDst - (unsigned char *)pDst_);
 }
 
-long CVariableInt::Compress(const void *pSrc_, int Size, void *pDst_, int DstSize)
+long CVariableInt::Compress(const void *pSrc_, int SrcSize, void *pDst_, int DstSize)
 {
-	int *pSrc = (int *)pSrc_;
+	dbg_assert(SrcSize % sizeof(int) == 0, "invalid bounds");
+
+	const int *pSrc = (int *)pSrc_;
 	unsigned char *pDst = (unsigned char *)pDst_;
-	unsigned char *pDstEnd = pDst + DstSize;
-	Size /= 4;
-	while(Size)
+	const unsigned char *pDstEnd = pDst + DstSize;
+	SrcSize /= sizeof(int);
+	while(SrcSize)
 	{
-		if(pDstEnd - pDst < 6)
+		if(pDstEnd - pDst <= MAX_BYTES_PACKED)
 			return -1;
 		pDst = CVariableInt::Pack(pDst, *pSrc);
-		Size--;
+		SrcSize--;
 		pSrc++;
 	}
-	return pDst - (unsigned char *)pDst_;
+	return (long)(pDst - (unsigned char *)pDst_);
 }
diff --git a/src/engine/shared/compression.h b/src/engine/shared/compression.h
index 93bff1246..f15615d6b 100644
--- a/src/engine/shared/compression.h
+++ b/src/engine/shared/compression.h
@@ -2,13 +2,21 @@
 /* If you are missing that file, acquire a complete release at teeworlds.com.                */
 #ifndef ENGINE_SHARED_COMPRESSION_H
 #define ENGINE_SHARED_COMPRESSION_H
+
 // variable int packing
 class CVariableInt
 {
 public:
+	enum
+	{
+		MAX_BYTES_PACKED = 5, // maximum number of bytes in a packed int
+	};
+
 	static unsigned char *Pack(unsigned char *pDst, int i);
 	static const unsigned char *Unpack(const unsigned char *pSrc, int *pInOut);
-	static long Compress(const void *pSrc, int Size, void *pDst, int DstSize);
-	static long Decompress(const void *pSrc, int Size, void *pDst, int DstSize);
+
+	static long Compress(const void *pSrc, int SrcSize, void *pDst, int DstSize);
+	static long Decompress(const void *pSrc, int SrcSize, void *pDst, int DstSize);
 };
+
 #endif
diff --git a/src/test/compression.cpp b/src/test/compression.cpp
new file mode 100644
index 000000000..f09e72feb
--- /dev/null
+++ b/src/test/compression.cpp
@@ -0,0 +1,68 @@
+#include <gtest/gtest.h>
+
+#include <engine/shared/compression.h>
+
+static const int DATA[] = {0, 1, -1, 32, 64, 256, -512, 12345, -123456, 1234567, 12345678, 123456789, 2147483647, (-2147483647 - 1)};
+static const int NUM = sizeof(DATA) / sizeof(int);
+static const int SIZES[NUM] = {1, 1, 1, 1, 2, 2, 2, 3, 3, 4, 4, 4, 5, 5};
+
+TEST(CVariableInt, RoundtripPackUnpack)
+{
+	for(int i = 0; i < NUM; i++)
+	{
+		unsigned char aPacked[CVariableInt::MAX_BYTES_PACKED];
+		int Result;
+		EXPECT_EQ(int(CVariableInt::Pack(aPacked, DATA[i]) - aPacked), SIZES[i]);
+		EXPECT_EQ(int(CVariableInt::Unpack(aPacked, &Result) - aPacked), SIZES[i]);
+		EXPECT_EQ(Result, DATA[i]);
+	}
+}
+
+TEST(CVariableInt, UnpackInvalid)
+{
+	unsigned char aPacked[CVariableInt::MAX_BYTES_PACKED];
+	for(int i = 0; i < CVariableInt::MAX_BYTES_PACKED; i++)
+		aPacked[i] = 0xFF;
+
+	int Result;
+	EXPECT_EQ(int(CVariableInt::Unpack(aPacked, &Result) - aPacked), int(CVariableInt::MAX_BYTES_PACKED));
+	EXPECT_EQ(Result, (-2147483647 - 1));
+
+	aPacked[0] &= ~0x40; // unset sign bit
+
+	EXPECT_EQ(int(CVariableInt::Unpack(aPacked, &Result) - aPacked), int(CVariableInt::MAX_BYTES_PACKED));
+	EXPECT_EQ(Result, 2147483647);
+}
+
+TEST(CVariableInt, RoundtripCompressDecompress)
+{
+	unsigned char aCompressed[NUM * CVariableInt::MAX_BYTES_PACKED];
+	int aDecompressed[NUM];
+	long ExpectedCompressedSize = 0;
+	for(int i = 0; i < NUM; i++)
+		ExpectedCompressedSize += SIZES[i];
+
+	long CompressedSize = CVariableInt::Compress(DATA, sizeof(DATA), aCompressed, sizeof(aCompressed));
+	ASSERT_EQ(CompressedSize, ExpectedCompressedSize);
+	long DecompressedSize = CVariableInt::Decompress(aCompressed, ExpectedCompressedSize, aDecompressed, sizeof(aDecompressed));
+	ASSERT_EQ(DecompressedSize, sizeof(DATA));
+	for(int i = 0; i < NUM; i++)
+	{
+		EXPECT_EQ(DATA[i], aDecompressed[i]);
+	}
+}
+
+TEST(CVariableInt, CompressBufferTooSmall)
+{
+	unsigned char aCompressed[NUM]; // too small
+	long CompressedSize = CVariableInt::Compress(DATA, sizeof(DATA), aCompressed, sizeof(aCompressed));
+	ASSERT_EQ(CompressedSize, -1);
+}
+
+TEST(CVariableInt, DecompressBufferTooSmall)
+{
+	unsigned char aCompressed[] = {0x00, 0x01, 0x40, 0x20, 0x80, 0x01, 0x80, 0x04, 0xFF, 0x07, 0xB9, 0xC0, 0x01};
+	int aUncompressed[4]; // too small
+	long CompressedSize = CVariableInt::Decompress(aCompressed, sizeof(aCompressed), aUncompressed, sizeof(aUncompressed));
+	ASSERT_EQ(CompressedSize, -1);
+}