diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 1bdfc94f5..153a1629e 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -245,6 +245,7 @@ target_compile_options(SRB2SDL2 PRIVATE
 	# This is a direct translation from versions.mk
 	$<$<AND:$<COMPILE_LANGUAGE:C>,$<C_COMPILER_ID:GNU>>:
 		-Wall
+		-Wextra
 		-Wno-trigraphs
 		-W # Was controlled by RELAXWARNINGS
 		-Wfloat-equal
@@ -329,7 +330,9 @@ target_compile_options(SRB2SDL2 PRIVATE
 	$<$<AND:$<COMPILE_LANGUAGE:C>,$<OR:$<C_COMPILER_ID:AppleClang>,$<C_COMPILER_ID:Clang>>>:
 		-Wall
 		-Wno-absolute-value
+		-Wextra
 		-Wno-trigraphs
+		-Wconditional-uninitialized
 		-Wno-error=non-literal-null-conversion
 		-Wno-error=constant-conversion
 		-Wno-error=unused-but-set-variable
@@ -346,6 +349,9 @@ target_compile_options(SRB2SDL2 PRIVATE
 	# C++, GNU, Clang and Apple Clang
 	$<$<AND:$<COMPILE_LANGUAGE:CXX>,$<OR:$<C_COMPILER_ID:GNU>,$<C_COMPILER_ID:AppleClang>,$<C_COMPILER_ID:Clang>>>:
 		-Wall
+		-Wextra
+		-Wno-trigraphs
+		-Wconditional-uninitialized
 	>
 
 	# C++, MSVC
diff --git a/src/blua/lvm.c b/src/blua/lvm.c
index b74fef4ee..627685b38 100644
--- a/src/blua/lvm.c
+++ b/src/blua/lvm.c
@@ -134,7 +134,7 @@ void luaV_gettable (lua_State *L, TValue *t, TValue *key, StkId val) {
 void luaV_settable (lua_State *L, TValue *t, TValue *key, StkId val) {
   int loop;
   for (loop = 0; loop < MAXTAGLOOP; loop++) {
-    TValue *tm;
+    TValue *tm = NULL;
     if (ttistable(t)) {  /* `t' is a table? */
       Table *h = hvalue(t);
       TValue *oldval = luaH_set(L, h, key); /* do a primitive set */
diff --git a/src/g_demo.c b/src/g_demo.c
index f64f34168..859ac5cba 100644
--- a/src/g_demo.c
+++ b/src/g_demo.c
@@ -1650,7 +1650,7 @@ static void G_LoadDemoExtraFiles(UINT8 **pp, UINT16 this_demo_version)
 	UINT16 totalfiles;
 	char filename[MAX_WADPATH];
 	UINT8 md5sum[16];
-	filestatus_t ncs;
+	filestatus_t ncs = FS_NOTFOUND;
 	boolean toomany = false;
 	boolean alreadyloaded;
 	UINT16 i, j;
diff --git a/src/g_game.c b/src/g_game.c
index 6a99381e7..0e7e2b344 100644
--- a/src/g_game.c
+++ b/src/g_game.c
@@ -5403,7 +5403,7 @@ void G_FreeMapSearch(mapsearchfreq_t *freq, INT32 freqc)
 INT32 G_FindMapByNameOrCode(const char *mapname, char **realmapnamep)
 {
 	boolean usemapcode = false;
-	INT32 newmapnum;
+	INT32 newmapnum = -1;
 	size_t mapnamelen = strlen(mapname);
 	char *p;
 
diff --git a/src/netcode/d_net.c b/src/netcode/d_net.c
index 5a2e229d3..b24409db1 100644
--- a/src/netcode/d_net.c
+++ b/src/netcode/d_net.c
@@ -940,7 +940,7 @@ void Command_Droprate(void)
 static boolean ShouldDropPacket(void)
 {
 	return (packetdropquantity[netbuffer->packettype])
-		|| (packetdroprate != 0 && rand() < (RAND_MAX * (packetdroprate / 100.f))) || packetdroprate == 100;
+		|| (packetdroprate != 0 && rand() < (((double)RAND_MAX) * (packetdroprate / 100.f))) || packetdroprate == 100;
 }
 #endif
 
diff --git a/src/p_user.c b/src/p_user.c
index 49b4b2c94..9fc1f8c9b 100644
--- a/src/p_user.c
+++ b/src/p_user.c
@@ -11307,7 +11307,7 @@ void P_DoTailsOverlay(player_t *player, mobj_t *tails)
 	fixed_t backwards = -1*FRACUNIT;
 	boolean doswim = (player->panim == PA_ABILITY && (player->mo->eflags & MFE_UNDERWATER));
 	boolean doroll = (player->panim == PA_ROLL || (player->panim == PA_JUMP && !(player->charflags & SF_NOJUMPSPIN)) || doswim);
-	angle_t rollangle;
+	angle_t rollangle = 0;
 	boolean panimchange;
 	INT32 ticnum = 0;
 	statenum_t chosenstate;
@@ -12089,7 +12089,7 @@ void P_PlayerThink(player_t *player)
 	// deez New User eXperiences.
 	{
 		angle_t oldang = player->drawangle, diff = 0;
-		UINT8 factor;
+		UINT8 factor = 0;
 		// Directionchar!
 		// Camera angle stuff.
 		if (player->exiting // no control, no modification
diff --git a/src/sdl/i_system.c b/src/sdl/i_system.c
index 173866e8b..97e77aa90 100644
--- a/src/sdl/i_system.c
+++ b/src/sdl/i_system.c
@@ -2857,7 +2857,7 @@ size_t I_GetRandomBytes(char *destination, size_t count)
 {
 #if defined (__unix__) || defined (UNIXCOMMON) || defined(__APPLE__)
 	FILE *rndsource;
-	size_t actual_bytes;
+	size_t actual_bytes = 0;
 
 	if (!(rndsource = fopen("/dev/urandom", "r")))
 		if (!(rndsource = fopen("/dev/random", "r")))
diff --git a/src/st_stuff.c b/src/st_stuff.c
index 342c7dcd8..b3e392499 100644
--- a/src/st_stuff.c
+++ b/src/st_stuff.c
@@ -815,7 +815,7 @@ static inline void ST_drawRings(void)
 
 static void ST_drawLivesArea(void)
 {
-	INT32 v_colmap = V_YELLOWMAP, livescount;
+	INT32 v_colmap = V_YELLOWMAP, livescount = -1;
 	boolean notgreyedout = false;
 
 	if (!stplyr->skincolor)