diff --git a/src/Make.pkg b/src/Make.pkg
index 62fb68d4b3f..f9711671acc 100644
--- a/src/Make.pkg
+++ b/src/Make.pkg
@@ -132,8 +132,7 @@ _cgo_export.o: _cgo_export.c _cgo_export.h
 # added _cgo_defun.$O to $OFILES, and added the installed copy of
 # package_x.so (built from x.cgo2.c) to $(INSTALLFILES).
 
-RUNTIME_CFLAGS_amd64=-D_64BIT
-RUNTIME_CFLAGS=-I"$(GOROOT)/src/pkg/runtime" $(RUNTIME_CFLAGS_$(GOARCH))
+RUNTIME_CFLAGS=-I"$(GOROOT)/src/pkg/runtime"
 
 # Have to run gcc with the right size argument on hybrid 32/64 machines.
 _CGO_CFLAGS_386=-m32
diff --git a/src/pkg/runtime/Makefile b/src/pkg/runtime/Makefile
index 58e0e76b51c..a208458ed78 100644
--- a/src/pkg/runtime/Makefile
+++ b/src/pkg/runtime/Makefile
@@ -12,13 +12,11 @@ SIZE_amd64=64
 SIZE_arm=32
 SIZE=$(SIZE_$(GOARCH))
 
-# Setup CFLAGS.  Add -D_64BIT on 64-bit platforms (sorry).
-CFLAGS_64=-D_64BIT
 # TODO(kaib): fix register allocation to honor extern register so we
 # can enable optimizations again.
 CFLAGS_arm=-N
 CFLAGS_windows=-D__WINDOWS__
-CFLAGS=-I$(GOOS) -I$(GOARCH) -I$(GOOS)/$(GOARCH) -wF $(CFLAGS_$(SIZE)) $(CFLAGS_$(GOARCH)) $(CFLAGS_$(GOOS))
+CFLAGS=-I$(GOOS) -I$(GOARCH) -I$(GOOS)/$(GOARCH) -wF $(CFLAGS_$(GOARCH)) $(CFLAGS_$(GOOS))
 
 GOFILES=\
 	debug.go\