diff -u --recursive spim-vanilla/Makefile spim/Makefile
--- spim-vanilla/Makefile	2011-11-22 16:03:37.000000000 -0600
+++ spim/Makefile	2011-11-22 20:31:46.639818922 -0600
@@ -81,20 +81,20 @@
 
 # SPIM needs flex's -I flag since the scanner is used interactively.
 # You can set the -8 flag so that funny characters do not hang the scanner.
-LEXFLAGS = -I -8
+LEXFLAGS += -I -8
 
 
 # If you use lex, set the variables this way:
 #MYLEX = lex
-#LEXFLAGS =
+#LEXFLAGS +=
 
 
 # SPIM works with either byacc or bison
 #YACC=byacc
-#YACCFLAGS = -d
+#YACCFLAGS += -d
 
 YACC=bison
-YFLAGS = -d --defines=parser_yacc.h --output=parser_yacc.c -p yy
+YFLAGS += -d --defines=parser_yacc.h --output=parser_yacc.c -p yy
 
 
 # Size of the segments when spim starts up (data segment must be >= 64K).
@@ -112,14 +112,14 @@
 DEFINES = $(MEM_SIZES) -DDEFAULT_EXCEPTION_HANDLER="\"$(EXCEPTION_DIR)/exceptions.s\""
 
 CC = g++
-CFLAGS = -I. -I$(CPU_DIR) $(DEFINES) -g -Wall -pedantic -Wextra -Wunused -Wno-write-strings -x c++
-YCFLAGS =
-LDFLAGS = -lm
+CFLAGS += -I. -I$(CPU_DIR) $(DEFINES) -g -Wall -pedantic -Wextra -Wunused -Wno-write-strings -x c++
+YCFLAGS +=
+LDFLAGS += -lm
 CSH = bash
 
 # lex.yy.c is usually compiled with -O to speed it up.
 
-LEXCFLAGS = -O $(CFLAGS)
+LEXCFLAGS += -O $(CFLAGS)