diff --git a/src/Makefile b/src/Makefile
index 9832fb63845727..0b87c7b8a6fae9 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -44,23 +44,34 @@ ifeq ($(OS),FreeBSD)
 FLAGS += -I$(LOCALBASE)/include
 endif
 
+# GC source code. It depends on which GC implementation to use.
+GC_SRCS := gc-common gc-stacks gc-alloc-profiler gc-heap-snapshot
+ifeq ($(WITH_MMTK), 1)
+GC_SRCS += gc-mmtk
+else
+GC_SRCS += gc-stock gc-debug gc-pages gc-page-profiler
+endif
+
 SRCS := \
 	jltypes gf typemap smallintset ast builtins module interpreter symbol \
 	dlload sys init task array genericmemory staticdata toplevel jl_uv datatype \
 	simplevector runtime_intrinsics precompile jloptions mtarraylist \
-	threading scheduler stackwalk gc-common gc-stock gc-mmtk gc-debug gc-pages gc-stacks gc-alloc-profiler gc-page-profiler \
-	method jlapi signal-handling safepoint timing subtype rtutils gc-heap-snapshot \
-	crc32c APInt-C processor ircode opaque_closure codegen-stubs coverage runtime_ccall engine
+	threading scheduler stackwalk \
+	method jlapi signal-handling safepoint timing subtype rtutils \
+	crc32c APInt-C processor ircode opaque_closure codegen-stubs coverage runtime_ccall engine \
+	$(GC_SRCS)
 
 RT_LLVMLINK :=
 CG_LLVMLINK :=
 
 ifeq ($(JULIACODEGEN),LLVM)
+GC_CODEGEN_SRCS := llvm-final-gc-lowering llvm-late-gc-lowering llvm-gc-invariant-verifier
 CODEGEN_SRCS := codegen jitlayers aotcompile debuginfo disasm llvm-simdloop \
-	llvm-final-gc-lowering llvm-pass-helpers llvm-late-gc-lowering llvm-ptls \
-	llvm-lower-handlers llvm-gc-invariant-verifier llvm-propagate-addrspaces \
+	llvm-pass-helpers llvm-ptls \
+	llvm-lower-handlers llvm-propagate-addrspaces \
 	llvm-multiversioning llvm-alloc-opt llvm-alloc-helpers cgmemmgr llvm-remove-addrspaces \
-	llvm-remove-ni llvm-julia-licm llvm-demote-float16 llvm-cpufeatures pipeline llvm_api
+	llvm-remove-ni llvm-julia-licm llvm-demote-float16 llvm-cpufeatures pipeline llvm_api \
+	$(GC_CODEGEN_SRCS)
 FLAGS += -I$(shell $(LLVM_CONFIG_HOST) --includedir)
 CG_LLVM_LIBS := all
 ifeq ($(USE_POLLY),1)
@@ -107,7 +118,12 @@ ifeq ($(USE_SYSTEM_LIBUV),0)
 UV_HEADERS += uv.h
 UV_HEADERS += uv/*.h
 endif
-PUBLIC_HEADERS := $(BUILDDIR)/julia_version.h $(wildcard $(SRCDIR)/support/*.h) $(addprefix $(SRCDIR)/,work-stealing-queue.h gc-interface.h gc-tls.h gc-tls-common.h gc-tls-mmtk.h julia.h julia_assert.h julia_threads.h julia_fasttls.h julia_locks.h julia_atomics.h jloptions.h)
+PUBLIC_HEADERS := $(BUILDDIR)/julia_version.h $(wildcard $(SRCDIR)/support/*.h) $(addprefix $(SRCDIR)/,work-stealing-queue.h gc-interface.h gc-tls-common.h julia.h julia_assert.h julia_threads.h julia_fasttls.h julia_locks.h julia_atomics.h jloptions.h)
+ifeq ($(WITH_MMTK), 1)
+	PUBLIC_HEADERS += $(addprefix $(SRCDIR)/,gc-tls-mmtk.h)
+else
+	PUBLIC_HEADERS += $(addprefix $(SRCDIR)/,gc-tls-stock.h)
+endif
 ifeq ($(OS),WINNT)
 PUBLIC_HEADERS += $(addprefix $(SRCDIR)/,win32_ucontext.h)
 endif
diff --git a/src/gc-debug.c b/src/gc-debug.c
index 2c8e1c60554143..7c479484cde45c 100644
--- a/src/gc-debug.c
+++ b/src/gc-debug.c
@@ -1,6 +1,5 @@
 // This file is a part of Julia. License is MIT: https://julialang.org/license
 
-#ifndef MMTK_GC
 #include "gc-common.h"
 #include "gc-stock.h"
 #include "julia.h"
@@ -1130,5 +1129,3 @@ void _report_gc_finished(uint64_t pause, uint64_t freed, int full, int recollect
 #ifdef __cplusplus
 }
 #endif
-
-#endif // !MMTK_GC
diff --git a/src/gc-mmtk.c b/src/gc-mmtk.c
index 65651f9c720db5..379e06ae08db84 100644
--- a/src/gc-mmtk.c
+++ b/src/gc-mmtk.c
@@ -1,5 +1,3 @@
-#ifdef MMTK_GC
-
 #include "gc-common.h"
 #include "mmtkMutator.h"
 #include "gc-mmtk.h"
@@ -1199,5 +1197,3 @@ JL_DLLEXPORT jl_value_t *jl_gc_internal_obj_base_ptr(void *p)
 #ifdef __cplusplus
 }
 #endif
-
-#endif // MMTK_GC
diff --git a/src/gc-mmtk.h b/src/gc-mmtk.h
index da84d38f8e9c52..826b21cd4945a9 100644
--- a/src/gc-mmtk.h
+++ b/src/gc-mmtk.h
@@ -1,5 +1,3 @@
-#ifdef MMTK_GC
-
 #include <stddef.h>
 #include <stdint.h>
 
@@ -29,5 +27,3 @@ JL_EXTENSION typedef struct _bigval_t {
 #ifdef __cplusplus
 }
 #endif
-
-#endif // MMTK_GC
diff --git a/src/gc-page-profiler.c b/src/gc-page-profiler.c
index e5c6b919787318..2625fa812781a7 100644
--- a/src/gc-page-profiler.c
+++ b/src/gc-page-profiler.c
@@ -1,6 +1,5 @@
 // This file is a part of Julia. License is MIT: https://julialang.org/license
 
-#ifndef MMTK_GC
 #include "gc-page-profiler.h"
 #include "julia.h"
 
@@ -179,5 +178,3 @@ JL_DLLEXPORT void jl_gc_take_page_profile(ios_t *stream)
 #ifdef __cplusplus
 }
 #endif
-
-#endif // !MMTK_GC
diff --git a/src/gc-pages.c b/src/gc-pages.c
index 976fc461d5b95c..71d59de29166f5 100644
--- a/src/gc-pages.c
+++ b/src/gc-pages.c
@@ -1,6 +1,5 @@
 // This file is a part of Julia. License is MIT: https://julialang.org/license
 
-#ifndef MMTK_GC
 #include "gc-common.h"
 #include "gc-stock.h"
 #ifndef _OS_WINDOWS_
@@ -206,5 +205,3 @@ void jl_gc_free_page(jl_gc_pagemeta_t *pg) JL_NOTSAFEPOINT
 #ifdef __cplusplus
 }
 #endif
-
-#endif // !MMTK_GC
diff --git a/src/gc-stacks.c b/src/gc-stacks.c
index a0ca2561c5cf95..d0a5d2a9683268 100644
--- a/src/gc-stacks.c
+++ b/src/gc-stacks.c
@@ -1,7 +1,6 @@
 // This file is a part of Julia. License is MIT: https://julialang.org/license
 
 #include "gc-common.h"
-#include "gc-stock.h"
 #include "threading.h"
 #ifndef _OS_WINDOWS_
 #  include <sys/resource.h>
diff --git a/src/gc-stock.c b/src/gc-stock.c
index c0bfc26cabc6bd..2cd7be078ae828 100644
--- a/src/gc-stock.c
+++ b/src/gc-stock.c
@@ -1,6 +1,5 @@
 // This file is a part of Julia. License is MIT: https://julialang.org/license
 
-#ifndef MMTK_GC
 #include "gc-common.h"
 #include "gc-stock.h"
 #include "gc-alloc-profiler.h"
@@ -4000,5 +3999,3 @@ JL_DLLEXPORT const char* jl_active_gc_impl(void) {
 #ifdef __cplusplus
 }
 #endif
-
-#endif // !MMTK_GC
diff --git a/src/gc-stock.h b/src/gc-stock.h
index 08b0999ed5c3a3..710c3adf46af3d 100644
--- a/src/gc-stock.h
+++ b/src/gc-stock.h
@@ -5,8 +5,6 @@
   . non-moving, precise mark and sweep collector
   . pool-allocates small objects, keeps big objects on a simple list
 */
-#ifndef MMTK_GC
-
 #ifndef JL_GC_H
 #define JL_GC_H
 
@@ -727,6 +725,3 @@ void _report_gc_finished(uint64_t pause, uint64_t freed, int full, int recollect
 #endif
 
 #endif
-
-
-#endif // !MMTK_GC
diff --git a/src/gc-tls-mmtk.h b/src/gc-tls-mmtk.h
index 7b1b249cd8ae3e..01791345b69843 100644
--- a/src/gc-tls-mmtk.h
+++ b/src/gc-tls-mmtk.h
@@ -1,7 +1,5 @@
 // This file is a part of Julia. License is MIT: https://julialang.org/license
 
-#ifdef MMTK_GC
-
 #include <assert.h>
 #include "mmtkMutator.h"
 
@@ -17,5 +15,3 @@ typedef struct {
 #ifdef __cplusplus
 }
 #endif
-
-#endif // MMTK_GC
diff --git a/src/gc-tls.h b/src/gc-tls-stock.h
similarity index 98%
rename from src/gc-tls.h
rename to src/gc-tls-stock.h
index dad914b8c11800..d82506383c5016 100644
--- a/src/gc-tls.h
+++ b/src/gc-tls-stock.h
@@ -1,7 +1,5 @@
 // This file is a part of Julia. License is MIT: https://julialang.org/license
 
-#ifndef MMTK_GC
-
 // Meant to be included in "julia_threads.h"
 #ifndef JL_GC_TLS_H
 #define JL_GC_TLS_H
@@ -68,5 +66,3 @@ typedef struct {
 #endif
 
 #endif // JL_GC_TLS_H
-
-#endif // MMTK_GC
diff --git a/src/julia_threads.h b/src/julia_threads.h
index f7b66aeb52f79b..b6ef65dc7fe52a 100644
--- a/src/julia_threads.h
+++ b/src/julia_threads.h
@@ -5,7 +5,7 @@
 #define JL_THREADS_H
 
 #ifndef MMTK_GC
-#include "gc-tls.h"
+#include "gc-tls-stock.h"
 #else
 #include "gc-tls-mmtk.h"
 #endif