--- a/Makefile
+++ b/Makefile
@@ -18,10 +18,8 @@
 
 # gcc with basic optimization (-march flag could
 # get overridden by architecture-specific builds)
-CC = gcc
-WARN_FLAGS = -Wall -W
-OPT_FLAGS = -O3 -fomit-frame-pointer -march=native \
-	    -D_FILE_OFFSET_BITS=64 -DNDEBUG -D_LARGEFILE64_SOURCE
+CFLAGS += -Wall -W
+CPPFLAGS += -D_FILE_OFFSET_BITS=64 -D_LARGEFILE64_SOURCE
 
 # use := instead of = so we only run the following once
 SVN_VERSION := $(shell svnversion .)
@@ -29,15 +27,14 @@
 	SVN_VERSION := unknown
 endif
 
-CFLAGS = $(OPT_FLAGS) $(MACHINE_FLAGS) $(WARN_FLAGS) \
-	 	-DMSIEVE_SVN_VERSION="\"$(SVN_VERSION)\"" \
-		-I. -Iaprcl -Iinclude -Ignfs -Ignfs/poly -Ignfs/poly/stage1
+CPPFLAGS += -DMSIEVE_SVN_VERSION="\"$(SVN_VERSION)\"" \
+	-I. -Iaprcl -Iinclude -Ignfs -Ignfs/poly -Ignfs/poly/stage1
 
 # tweak the compile flags
 
 ifeq ($(ECM),1)
-	CFLAGS += -DHAVE_GMP_ECM
-	LIBS += -lecm
+	CPPFLAGS += -DHAVE_GMP_ECM
+	LIBS += -lecm -lgomp
 endif
 ifeq ($(WIN),1)
 
@@ -61,22 +58,21 @@
 	CUDA_ROOT = $(shell dirname $(NVCC))/../
 	CUDA_LIBS = -lcuda
 endif
-	CFLAGS += -I"$(CUDA_ROOT)/include" -Icub -DHAVE_CUDA
+	CPPFLAGS += -I"$(CUDA_ROOT)/include" -Icub -DHAVE_CUDA
 	LIBS += $(CUDA_LIBS)
 endif
 ifeq ($(MPI),1)
-	CC = mpicc
-	CFLAGS += -DHAVE_MPI
+	CPPFLAGS += -DHAVE_MPI
 endif
 ifeq ($(BOINC),1)
 	# fill in as appropriate
 	BOINC_INC_DIR = .
 	BOINC_LIB_DIR = .
-	CFLAGS += -I$(BOINC_INC_DIR) -DHAVE_BOINC
+	CPPFLAGS += -I$(BOINC_INC_DIR) -DHAVE_BOINC
 	LIBS += -L$(BOINC_LIB_DIR) -lboinc_api -lboinc
 endif
 ifeq ($(NO_ZLIB),1)
-	CFLAGS += -DNO_ZLIB
+	CPPFLAGS += -DNO_ZLIB
 else
 	LIBS += -lz
 endif
@@ -272,9 +268,9 @@
 
 all: $(COMMON_OBJS) $(QS_OBJS) $(NFS_OBJS) $(GPU_OBJS)
 	rm -f libmsieve.a
-	ar r libmsieve.a $(COMMON_OBJS) $(QS_OBJS) $(NFS_OBJS)
-	ranlib libmsieve.a
-	$(CC) $(CFLAGS) demo.c -o msieve $(LDFLAGS) \
+	$(AR) r libmsieve.a $(COMMON_OBJS) $(QS_OBJS) $(NFS_OBJS)
+	$(RANLIB) libmsieve.a
+	$(CC) $(LDFLAGS) $(CFLAGS) $(CPPFLAGS) demo.c -o msieve \
 			libmsieve.a $(LIBS)
 
 clean:
@@ -287,27 +283,27 @@
 # common file build rules
 
 %.o: %.c $(COMMON_HDR)
-	$(CC) $(CFLAGS) -c -o $@ $<
+	$(CC) $(CFLAGS) $(CPPFLAGS) -c -o $@ $<
 
 # QS build rules
 
 mpqs/sieve_core_generic_32k.qo: mpqs/sieve_core.c $(COMMON_HDR) $(QS_HDR)
-	$(CC) $(CFLAGS) -DBLOCK_KB=32 -DHAS_SSE2 \
+	$(CC) $(CFLAGS) $(CPPFLAGS) -DBLOCK_KB=32 -DHAS_SSE2 \
 		-DROUTINE_NAME=qs_core_sieve_generic_32k \
 		-c -o $@ mpqs/sieve_core.c
 
 mpqs/sieve_core_generic_64k.qo: mpqs/sieve_core.c $(COMMON_HDR) $(QS_HDR)
-	$(CC) $(CFLAGS) -DBLOCK_KB=64 -DHAS_SSE2 \
+	$(CC) $(CFLAGS) $(CPPFLAGS) -DBLOCK_KB=64 -DHAS_SSE2 \
 		-DROUTINE_NAME=qs_core_sieve_generic_64k \
 		-c -o $@ mpqs/sieve_core.c
 
 %.qo: %.c $(COMMON_HDR) $(QS_HDR)
-	$(CC) $(CFLAGS) -c -o $@ $<
+	$(CC) $(CFLAGS) $(CPPFLAGS) -c -o $@ $<
 
 # NFS build rules
 
 %.no: %.c $(COMMON_HDR) $(NFS_HDR)
-	$(CC) $(CFLAGS) -Ignfs -c -o $@ $<
+	$(CC) $(CFLAGS) $(CPPFLAGS) -Ignfs -c -o $@ $<
 
 # GPU build rules