diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 455ce611b..574aff995 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -485,7 +485,8 @@ set( PLAT_WIN32_SOURCES
 	win32/win32gliface.cpp
 	win32/win32video.cpp )
 set( PLAT_POSIX_SOURCES
-	posix/i_steam.cpp )
+	posix/i_steam.cpp
+	posix/i_system_posix.cpp )
 set( PLAT_SDL_SOURCES
 	posix/sdl/crashcatcher.c
 	posix/sdl/hardware.cpp
diff --git a/src/posix/cocoa/i_system.mm b/src/posix/cocoa/i_system.mm
index 66f51eea6..8535abc69 100644
--- a/src/posix/cocoa/i_system.mm
+++ b/src/posix/cocoa/i_system.mm
@@ -33,41 +33,16 @@
 
 #include "i_common.h"
 
-#include <fnmatch.h>
-#include <unistd.h>
-#include <sys/stat.h>
 #include <sys/sysctl.h>
 
-#include "d_protocol.h"
-#include "doomdef.h"
-#include "doomerrors.h"
-#include "doomstat.h"
-#include "g_game.h"
-#include "gameconfigfile.h"
-#include "i_sound.h"
 #include "i_system.h"
 #include "st_console.h"
 #include "v_text.h"
-#include "x86.h"
-#include "cmdlib.h"
-
-
-void I_Tactile(int /*on*/, int /*off*/, int /*total*/)
-{
-}
-
-
-ticcmd_t* I_BaseTiccmd()
-{
-	static ticcmd_t emptycmd;
-	return &emptycmd;
-}
-
 
 
 double PerfToSec, PerfToMillisec;
 
-static void CalculateCPUSpeed()
+void CalculateCPUSpeed()
 {
 	long long frequency;
 	size_t size = sizeof frequency;
@@ -84,17 +59,6 @@ static void CalculateCPUSpeed()
 	}
 }
 
-void I_Init(void)
-{
-	CheckCPUID(&CPU);
-	CalculateCPUSpeed();
-	DumpCPUInfo(&CPU);
-}
-
-void I_SetIWADInfo()
-{
-}
-
 
 void I_DebugPrint(const char *cp)
 {
@@ -174,90 +138,6 @@ int I_PickIWad(WadStuff* const wads, const int numwads, const bool showwin, cons
 }
 
 
-bool I_WriteIniFailed()
-{
-	printf("The config file %s could not be saved:\n%s\n", GameConfig->GetPathName(), strerror(errno));
-	return false; // return true to retry
-}
-
-
-static const char *pattern;
-
-#if MAC_OS_X_VERSION_MAX_ALLOWED < 1080
-static int matchfile(struct dirent *ent)
-#else
-static int matchfile(const struct dirent *ent)
-#endif
-{
-	return fnmatch(pattern, ent->d_name, FNM_NOESCAPE) == 0;
-}
-
-void* I_FindFirst(const char* const filespec, findstate_t* const fileinfo)
-{
-	FString dir;
-	
-	const char* const slash = strrchr(filespec, '/');
-
-	if (slash)
-	{
-		pattern = slash+1;
-		dir = FString(filespec, slash - filespec + 1);
-	}
-	else
-	{
-		pattern = filespec;
-		dir = ".";
-	}
-
-	fileinfo->current = 0;
-	fileinfo->count = scandir(dir.GetChars(), &fileinfo->namelist, matchfile, alphasort);
-
-	if (fileinfo->count > 0)
-	{
-		return fileinfo;
-	}
-
-	return (void*)-1;
-}
-
-int I_FindNext(void* const handle, findstate_t* const fileinfo)
-{
-	findstate_t* const state = static_cast<findstate_t*>(handle);
-
-	if (state->current < fileinfo->count)
-	{
-		return ++state->current < fileinfo->count ? 0 : -1;
-	}
-
-	return -1;
-}
-
-int I_FindClose(void* const handle)
-{
-	findstate_t* const state = static_cast<findstate_t*>(handle);
-
-	if (handle != (void*)-1 && state->count > 0)
-	{
-		for (int i = 0; i < state->count; ++i)
-		{
-			free(state->namelist[i]);
-		}
-
-		free(state->namelist);
-		state->namelist = NULL;
-		state->count = 0;
-	}
-
-	return 0;
-}
-
-int I_FindAttr(findstate_t* const fileinfo)
-{
-	dirent* const ent = fileinfo->namelist[fileinfo->current];
-	return (ent->d_type & DT_DIR) ? FA_DIREC : 0;
-}
-
-
 void I_PutInClipboard(const char* const string)
 {
 	NSPasteboard* const pasteBoard = [NSPasteboard generalPasteboard];
@@ -289,11 +169,3 @@ unsigned int I_MakeRNGSeed()
 {
 	return static_cast<unsigned int>(arc4random());
 }
-
-
-TArray<FString> I_GetGogPaths()
-{
-	// GOG's Doom games are Windows only at the moment
-	return TArray<FString>();
-}
-
diff --git a/src/posix/i_system_posix.cpp b/src/posix/i_system_posix.cpp
new file mode 100644
index 000000000..7c6514395
--- /dev/null
+++ b/src/posix/i_system_posix.cpp
@@ -0,0 +1,153 @@
+//-----------------------------------------------------------------------------
+//
+// Copyright 1993-1996 id Software
+// Copyright 1999-2016 Randy Heit
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see http://www.gnu.org/licenses/
+//
+//-----------------------------------------------------------------------------
+//
+
+#include <stdio.h>
+#include <errno.h>
+#include <fnmatch.h>
+
+#ifdef __APPLE__
+#include <AvailabilityMacros.h>
+#endif // __APPLE__
+
+#include "d_protocol.h"
+#include "i_system.h"
+#include "gameconfigfile.h"
+#include "x86.h"
+
+
+void I_Tactile(int /*on*/, int /*off*/, int /*total*/)
+{
+}
+
+static ticcmd_t emptycmd;
+
+ticcmd_t *I_BaseTiccmd()
+{
+	return &emptycmd;
+}
+
+//
+// I_Init
+//
+void I_Init()
+{
+	extern void CalculateCPUSpeed();
+
+	CheckCPUID(&CPU);
+	CalculateCPUSpeed();
+	DumpCPUInfo(&CPU);
+}
+
+
+void I_SetIWADInfo()
+{
+}
+
+
+bool I_WriteIniFailed()
+{
+	printf("The config file %s could not be saved:\n%s\n", GameConfig->GetPathName(), strerror(errno));
+	return false; // return true to retry
+}
+
+
+static const char *pattern;
+
+#if defined(__APPLE__) && MAC_OS_X_VERSION_MAX_ALLOWED < 1080
+static int matchfile(struct dirent *ent)
+#else
+static int matchfile(const struct dirent *ent)
+#endif
+{
+	return fnmatch(pattern, ent->d_name, FNM_NOESCAPE) == 0;
+}
+
+void *I_FindFirst(const char *const filespec, findstate_t *const fileinfo)
+{
+	FString dir;
+
+	const char *const slash = strrchr(filespec, '/');
+
+	if (slash)
+	{
+		pattern = slash + 1;
+		dir = FString(filespec, slash - filespec + 1);
+	}
+	else
+	{
+		pattern = filespec;
+		dir = ".";
+	}
+
+	fileinfo->current = 0;
+	fileinfo->count = scandir(dir.GetChars(), &fileinfo->namelist, matchfile, alphasort);
+
+	if (fileinfo->count > 0)
+	{
+		return fileinfo;
+	}
+
+	return (void *)-1;
+}
+
+int I_FindNext(void *const handle, findstate_t *const fileinfo)
+{
+	findstate_t *const state = static_cast<findstate_t *>(handle);
+
+	if (state->current < fileinfo->count)
+	{
+		return ++state->current < fileinfo->count ? 0 : -1;
+	}
+
+	return -1;
+}
+
+int I_FindClose(void *const handle)
+{
+	findstate_t *const state = static_cast<findstate_t *>(handle);
+
+	if (handle != (void *)-1 && state->count > 0)
+	{
+		for (int i = 0; i < state->count; ++i)
+		{
+			free(state->namelist[i]);
+		}
+
+		free(state->namelist);
+		state->namelist = nullptr;
+		state->count = 0;
+	}
+
+	return 0;
+}
+
+int I_FindAttr(findstate_t *const fileinfo)
+{
+	dirent *const ent = fileinfo->namelist[fileinfo->current];
+	return (ent->d_type & DT_DIR) ? FA_DIREC : 0;
+}
+
+
+TArray<FString> I_GetGogPaths()
+{
+	// GOG's Doom games are Windows only at the moment
+	return TArray<FString>();
+}
diff --git a/src/posix/sdl/i_system.cpp b/src/posix/sdl/i_system.cpp
index 88b2748c7..991682fec 100644
--- a/src/posix/sdl/i_system.cpp
+++ b/src/posix/sdl/i_system.cpp
@@ -19,60 +19,17 @@
 //-----------------------------------------------------------------------------
 //
 
-
-#include <stdlib.h>
-#include <stdio.h>
-#include <string.h>
-#include <fnmatch.h>
-#include <unistd.h>
-
-#include <stdarg.h>
-#include <sys/types.h>
-#include <sys/time.h>
-#include <sys/stat.h>
-#include <sys/wait.h>
 #include <fcntl.h>
-#include <signal.h>
+#include <time.h>
+#include <unistd.h>
 
 #include <SDL.h>
 
-#include "doomerrors.h"
-#include <math.h>
-
-#include "doomtype.h"
-#include "doomstat.h"
+#include "d_main.h"
+#include "i_system.h"
 #include "version.h"
-#include "doomdef.h"
-#include "cmdlib.h"
-#include "m_argv.h"
-#include "m_misc.h"
-#include "i_video.h"
-#include "i_sound.h"
-#include "i_music.h"
 #include "x86.h"
 
-#include "d_main.h"
-#include "d_net.h"
-#include "g_game.h"
-#include "i_system.h"
-#include "c_dispatch.h"
-#include "templates.h"
-#include "v_palette.h"
-#include "textures.h"
-#include "bitmap.h"
-
-#include "stats.h"
-#include "hardware.h"
-#include "gameconfigfile.h"
-
-#include "m_fixed.h"
-#include "g_level.h"
-
-extern "C"
-{
-	double		SecondsPerCycle = 1e-8;
-	double		CyclesPerSecond = 1e8;
-}
 
 #ifndef NO_GTK
 bool I_GtkAvailable ();
@@ -84,38 +41,9 @@ int I_PickIWad_Cocoa (WadStuff *wads, int numwads, bool showwin, int defaultiwad
 
 double PerfToSec, PerfToMillisec;
 
-void I_Tactile (int /*on*/, int /*off*/, int /*total*/)
-{
-}
-
-ticcmd_t emptycmd;
-ticcmd_t *I_BaseTiccmd(void)
-{
-	return &emptycmd;
-}
-
-void I_BeginRead(void)
-{
-}
-
-void I_EndRead(void)
-{
-}
-
-
-//
-// I_Init
-//
-void I_Init (void)
-{
-	CheckCPUID (&CPU);
-	DumpCPUInfo (&CPU);
-}
-
 //
 // I_Error
 //
-extern FILE *Logfile;
 
 #ifdef __APPLE__
 void Mac_I_FatalError(const char* errortext);
@@ -164,11 +92,9 @@ void I_ShowFatalError(const char *message)
 #else
 	// ???
 #endif
-	
 }
 
-	
-void I_SetIWADInfo ()
+void CalculateCPUSpeed()
 {
 }
 
@@ -295,80 +221,6 @@ int I_PickIWad (WadStuff *wads, int numwads, bool showwin, int defaultiwad)
 	return i-1;
 }
 
-bool I_WriteIniFailed ()
-{
-	printf ("The config file %s could not be saved:\n%s\n", GameConfig->GetPathName(), strerror(errno));
-	return false;
-	// return true to retry
-}
-
-static const char *pattern;
-
-#if defined(__APPLE__) && MAC_OS_X_VERSION_MAX_ALLOWED < 1080
-static int matchfile (struct dirent *ent)
-#else
-static int matchfile (const struct dirent *ent)
-#endif
-{
-	return fnmatch (pattern, ent->d_name, FNM_NOESCAPE) == 0;
-}
-
-void *I_FindFirst (const char *filespec, findstate_t *fileinfo)
-{
-	FString dir;
-	
-	const char *slash = strrchr (filespec, '/');
-	if (slash)
-	{
-		pattern = slash+1;
-		dir = FString(filespec, slash-filespec+1);
-	}
-	else
-	{
-		pattern = filespec;
-		dir = ".";
-	}
-
-	fileinfo->current = 0;
-	fileinfo->count = scandir (dir.GetChars(), &fileinfo->namelist,
-							   matchfile, alphasort);
-	if (fileinfo->count > 0)
-	{
-		return fileinfo;
-	}
-	return (void*)-1;
-}
-
-int I_FindNext (void *handle, findstate_t *fileinfo)
-{
-	findstate_t *state = (findstate_t *)handle;
-	if (state->current < fileinfo->count)
-	{
-		return ++state->current < fileinfo->count ? 0 : -1;
-	}
-	return -1;
-}
-
-int I_FindClose (void *handle)
-{
-	findstate_t *state = (findstate_t *)handle;
-	if (handle != (void*)-1 && state->count > 0)
-	{
-		for(int i = 0;i < state->count;++i)
-			free (state->namelist[i]);
-		state->count = 0;
-		free (state->namelist);
-		state->namelist = NULL;
-	}
-	return 0;
-}
-
-int I_FindAttr(findstate_t* const fileinfo)
-{
-	dirent* const ent = fileinfo->namelist[fileinfo->current];
-	return (ent->d_type & DT_DIR) ? FA_DIREC : 0;
-}
-
 void I_PutInClipboard (const char *str)
 {
 	SDL_SetClipboardText(str);
@@ -406,10 +258,3 @@ unsigned int I_MakeRNGSeed()
 	}
 	return seed;
 }
-
-TArray<FString> I_GetGogPaths()
-{
-	// GOG's Doom games are Windows only at the moment
-	return TArray<FString>();
-}
-