diff --git a/Makefile b/Makefile
index 1ead1c6ce..3198db7ee 100644
--- a/Makefile
+++ b/Makefile
@@ -278,10 +278,12 @@ rvfi_preserve_fns=-c_preserve rvfi_set_instr_packet \
   -c_preserve print_instr_packet \
   -c_preserve print_rvfi_exec
 
+# sed -i isn't posix compliant, unfortunately
 generated_definitions/c/riscv_rvfi_model_$(ARCH).c: $(SAIL_RVFI_SRCS) model/main.sail Makefile
 	mkdir -p generated_definitions/c
 	$(SAIL) $(rvfi_preserve_fns) $(SAIL_FLAGS) -O -Oconstant_fold -memo_z3 -c -c_include riscv_prelude.h -c_include riscv_platform.h -c_no_main $(SAIL_RVFI_SRCS) model/main.sail -o $(basename $@)
-	sed -i -e '/^[[:space:]]*$$/d' $@
+	sed -e '/^[[:space:]]*$$/d' $@ > $@.new
+	mv $@.new $@
 
 c_emulator/riscv_rvfi_$(ARCH): generated_definitions/c/riscv_rvfi_model_$(ARCH).c $(C_INCS) $(C_SRCS) $(SOFTFLOAT_LIBS) Makefile
 	gcc -g $(C_WARNINGS) $(C_FLAGS) $< -DRVFI_DII $(C_SRCS) $(SAIL_LIB_DIR)/*.c $(C_LIBS) -o $@
@@ -311,14 +313,18 @@ generated_definitions/lem/$(ARCH)/riscv.lem: $(SAIL_SRCS) Makefile
 	$(SAIL) $(SAIL_FLAGS) -lem -lem_output_dir generated_definitions/lem/$(ARCH) -isa_output_dir generated_definitions/isabelle/$(ARCH) -o riscv -lem_mwords -lem_lib Riscv_extras -lem_lib Riscv_extras_fdext -lem_lib Mem_metadata $(SAIL_SRCS)
 	echo "declare {isabelle} rename field sync_exception_ext = sync_exception_ext_exception" >> generated_definitions/lem/$(ARCH)/riscv_types.lem
 
+# sed -i isn't posix compliant, unfortunately
 generated_definitions/isabelle/$(ARCH)/Riscv.thy: generated_definitions/isabelle/$(ARCH)/ROOT generated_definitions/lem/$(ARCH)/riscv.lem $(RISCV_EXTRAS_LEM) Makefile
 	lem -isa -outdir generated_definitions/isabelle/$(ARCH) -lib Sail=$(SAIL_SRC_DIR)/lem_interp -lib Sail=$(SAIL_SRC_DIR)/gen_lib \
 		$(RISCV_EXTRAS_LEM) \
 		generated_definitions/lem/$(ARCH)/riscv_types.lem \
 		generated_definitions/lem/$(ARCH)/riscv.lem
-	sed -i 's/datatype ast/datatype (plugins only: size) ast/' generated_definitions/isabelle/$(ARCH)/Riscv_types.thy
-	sed -i "s/record( 'asidlen, 'valen, 'palen, 'ptelen) TLB_Entry/record (overloaded) ( 'asidlen, 'valen, 'palen, 'ptelen) TLB_Entry/" generated_definitions/isabelle/$(ARCH)/Riscv_types.thy
-	sed -i "s/by pat_completeness auto/by pat_completeness (auto intro!: let_cong bind_cong MemoryOpResult.case_cong)/" generated_definitions/isabelle/$(ARCH)/Riscv.thy
+	sed 's/datatype ast/datatype (plugins only: size) ast/' generated_definitions/isabelle/$(ARCH)/Riscv_types.thy >  generated_definitions/isabelle/$(ARCH)/Riscv_types.thy.new
+	mv  generated_definitions/isabelle/$(ARCH)/Riscv_types.thy.new generated_definitions/isabelle/$(ARCH)/Riscv_types.thy
+	sed "s/record( 'asidlen, 'valen, 'palen, 'ptelen) TLB_Entry/record (overloaded) ( 'asidlen, 'valen, 'palen, 'ptelen) TLB_Entry/" generated_definitions/isabelle/$(ARCH)/Riscv_types.thy > generated_definitions/isabelle/$(ARCH)/Riscv_types.thy.new
+	mv generated_definitions/isabelle/$(ARCH)/Riscv_types.thy.new generated_definitions/isabelle/$(ARCH)/Riscv_types.thy
+	sed "s/by pat_completeness auto/by pat_completeness (auto intro!: let_cong bind_cong MemoryOpResult.case_cong)/" generated_definitions/isabelle/$(ARCH)/Riscv.thy > generated_definitions/isabelle/$(ARCH)/Riscv.thy.new
+	mv generated_definitions/isabelle/$(ARCH)/Riscv.thy.new generated_definitions/isabelle/$(ARCH)/Riscv.thy
 
 generated_definitions/hol4/$(ARCH)/Holmakefile: handwritten_support/Holmakefile
 	mkdir -p generated_definitions/hol4/$(ARCH)