diff --git a/src/Makefile b/src/Makefile
index f43e3c24..f7a8c1b8 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -366,7 +366,12 @@ ifdef DEBUGMODE
 
 	# build with debugging information
 	WINDRESFLAGS = -D_DEBUG
-	CFLAGS+=-O0 -Wall -DPARANOIA -DRANGECHECK
+ifdef GCC48
+	CFLAGS+=-Og
+else
+	CFLAGS+=-O0
+endif
+	CFLAGS+= -Wall -DPARANOIA -DRANGECHECK
 else
 
 
diff --git a/src/am_map.c b/src/am_map.c
index 90f81572..b28cecf1 100644
--- a/src/am_map.c
+++ b/src/am_map.c
@@ -999,7 +999,7 @@ static inline void AM_drawWalls(void)
 	static mline_t l;
 #ifdef ESLOPE
 	fixed_t frontf1,frontf2, frontc1, frontc2; // front floor/ceiling ends
-	fixed_t backf1, backf2, backc1, backc2; // back floor ceiling ends
+	fixed_t backf1 = 0, backf2 = 0, backc1 = 0, backc2 = 0; // back floor ceiling ends
 #endif
 
 	for (i = 0; i < numlines; i++)