diff --git a/public/tier0/basetypes.h b/public/tier0/basetypes.h
index 541b69d7..ccf15dcd 100644
--- a/public/tier0/basetypes.h
+++ b/public/tier0/basetypes.h
@@ -37,8 +37,10 @@
 #endif
 
 
-#ifdef _LINUX
+#if defined _LINUX && !defined __APPLE__
 typedef unsigned int uintptr_t;
+#elif defined __APPLE__
+#include <stdint.h>
 #endif
 
 #define ExecuteNTimes( nTimes, x )	\
@@ -68,6 +70,9 @@ inline T AlignValue( T val, unsigned alignment )
 	( ((number) + ((boundary)-1)) / (boundary) ) * (boundary)
 
 // In case this ever changes
+#if defined M_PI
+# undef M_PI
+#endif
 #define M_PI			3.14159265358979323846
 
 #include "valve_minmax_on.h"
@@ -103,7 +108,9 @@ typedef unsigned char BYTE;
 typedef unsigned char byte;
 typedef unsigned short word;
 
+#if !defined __APPLE__
 typedef unsigned int uintptr_t;
+#endif
 
 
 enum ThreeState_t
diff --git a/public/tier0/memalloc.h b/public/tier0/memalloc.h
index b1ccbf1d..eb001b68 100644
--- a/public/tier0/memalloc.h
+++ b/public/tier0/memalloc.h
@@ -117,7 +117,7 @@ inline void *MemAlloc_AllocAligned( size_t size, size_t align )
 {
 	unsigned char *pAlloc, *pResult;
 
-	if (!IsPowerOfTwo(align))
+	if (!IsPowerOfTwo(uint(align)))
 		return NULL;
 
 	align = (align > sizeof(void *) ? align : sizeof(void *)) - 1;
@@ -135,7 +135,7 @@ inline void *MemAlloc_AllocAligned( size_t size, size_t align, const char *pszFi
 {
 	unsigned char *pAlloc, *pResult;
 
-	if (!IsPowerOfTwo(align))
+	if (!IsPowerOfTwo(uint(align)))
 		return NULL;
 
 	align = (align > sizeof(void *) ? align : sizeof(void *)) - 1;
@@ -151,7 +151,7 @@ inline void *MemAlloc_AllocAligned( size_t size, size_t align, const char *pszFi
 
 inline void *MemAlloc_ReallocAligned( void *ptr, size_t size, size_t align )
 {
-	if ( !IsPowerOfTwo( align ) )
+	if ( !IsPowerOfTwo( uint(align) ) )
 		return NULL;
 
 	// Don't change alignment between allocation + reallocation.
diff --git a/public/tier0/memdbgon.h b/public/tier0/memdbgon.h
index 59ad4675..b269ccd4 100644
--- a/public/tier0/memdbgon.h
+++ b/public/tier0/memdbgon.h
@@ -29,7 +29,11 @@
 #include <wchar.h>
 #endif
 #include <string.h>
+#if defined __APPLE__
+#include <stdlib.h>
+#else
 #include <malloc.h>
+#endif
 #include "commonmacros.h"
 #include "memalloc.h"
 
diff --git a/public/tier0/platform.h b/public/tier0/platform.h
index 0da9e564..8b21a079 100644
--- a/public/tier0/platform.h
+++ b/public/tier0/platform.h
@@ -42,7 +42,11 @@
 #include <alloca.h>
 #endif // _LINUX
 
+#if defined __APPLE__
+#include <stdlib.h>
+#else
 #include <malloc.h>
+#endif
 #ifdef _MSC_VER
 #include <new.h>
 #elif defined __GNUC__
diff --git a/public/tier0/threadtools.h b/public/tier0/threadtools.h
index 130dbfc0..eead39ed 100644
--- a/public/tier0/threadtools.h
+++ b/public/tier0/threadtools.h
@@ -1410,6 +1410,9 @@ inline CThreadMutex::CThreadMutex()
 {
 	// enable recursive locks as we need them
 	pthread_mutexattr_init( &m_Attr );
+#if defined __APPLE__
+# define PTHREAD_MUTEX_RECURSIVE_NP PTHREAD_MUTEX_RECURSIVE
+#endif
 	pthread_mutexattr_settype( &m_Attr, PTHREAD_MUTEX_RECURSIVE_NP );
 	pthread_mutex_init( &m_Mutex, &m_Attr );
 }
diff --git a/public/tier1/KeyValues.h b/public/tier1/KeyValues.h
index 52856d64..7eb2f026 100644
--- a/public/tier1/KeyValues.h
+++ b/public/tier1/KeyValues.h
@@ -167,8 +167,8 @@ public:
 	void SetColor( const char *keyName, Color value);
 
 	// Memory allocation (optimized)
-	void *operator new( unsigned int iAllocSize );
-	void *operator new( unsigned int iAllocSize, int nBlockUse, const char *pFileName, int nLine );
+	void *operator new( size_t iAllocSize );
+	void *operator new( size_t iAllocSize, int nBlockUse, const char *pFileName, int nLine );
 	void operator delete( void *pMem );
 	void operator delete( void *pMem, int nBlockUse, const char *pFileName, int nLine );
 
diff --git a/tier1/KeyValues.cpp b/tier1/KeyValues.cpp
index e8ba3e54..ad08e5f3 100644
--- a/tier1/KeyValues.cpp
+++ b/tier1/KeyValues.cpp
@@ -2340,13 +2340,13 @@ bool KeyValues::ReadAsBinary( CUtlBuffer &buffer )
 //-----------------------------------------------------------------------------
 // Purpose: memory allocator
 //-----------------------------------------------------------------------------
-void *KeyValues::operator new( unsigned int iAllocSize )
+void *KeyValues::operator new( size_t iAllocSize )
 {
 	MEM_ALLOC_CREDIT();
 	return KeyValuesSystem()->AllocKeyValuesMemory(iAllocSize);
 }
 
-void *KeyValues::operator new( unsigned int iAllocSize, int nBlockUse, const char *pFileName, int nLine )
+void *KeyValues::operator new( size_t iAllocSize, int nBlockUse, const char *pFileName, int nLine )
 {
 	MemAlloc_PushAllocDbgInfo( pFileName, nLine );
 	void *p = KeyValuesSystem()->AllocKeyValuesMemory(iAllocSize);