diff --git a/repos/base-fiasco/lib/mk/core-fiasco.inc b/repos/base-fiasco/lib/mk/core-fiasco.inc
index 98189f8bc2..83926058ac 100644
--- a/repos/base-fiasco/lib/mk/core-fiasco.inc
+++ b/repos/base-fiasco/lib/mk/core-fiasco.inc
@@ -1,4 +1,5 @@
-GEN_CORE_DIR = $(BASE_DIR)/src/core
+GEN_CORE_DIR := $(dir $(call select_from_repositories,src/core/main.cc))
+GEN_SRC_DIR  := $(realpath $(GEN_CORE_DIR)/..)
 
 SRC_CC      += stack_area.cc \
                core_log.cc \
@@ -40,7 +41,7 @@ SRC_CC      += stack_area.cc \
 INC_DIR     += $(REP_DIR)/src/core/include \
                $(GEN_CORE_DIR)/include \
                $(REP_DIR)/src/include \
-               $(BASE_DIR)/src/include
+               $(GEN_SRC_DIR)/include
 
 LIBS        += base-fiasco-common syscall-fiasco cxx
 
@@ -70,4 +71,3 @@ vpath default_log.cc              $(GEN_CORE_DIR)
 vpath dump_alloc.cc               $(GEN_CORE_DIR)
 vpath stack_area.cc               $(GEN_CORE_DIR)
 vpath pager_ep.cc                 $(GEN_CORE_DIR)
-vpath %.cc                        $(REP_DIR)/src/core
diff --git a/repos/base-fiasco/lib/mk/spec/x86_32/core-fiasco.mk b/repos/base-fiasco/lib/mk/spec/x86_32/core-fiasco.mk
index 7a7faeb157..ed5da33137 100644
--- a/repos/base-fiasco/lib/mk/spec/x86_32/core-fiasco.mk
+++ b/repos/base-fiasco/lib/mk/spec/x86_32/core-fiasco.mk
@@ -7,3 +7,4 @@ vpath io_port_session_component.cc $(GEN_CORE_DIR)/spec/x86
 vpath io_port_session_support.cc   $(GEN_CORE_DIR)/spec/x86
 vpath platform_services.cc         $(GEN_CORE_DIR)/spec/x86
 vpath platform_x86.cc              $(REP_DIR)/src/core/spec/x86
+vpath %.cc                         $(REP_DIR)/src/core
diff --git a/repos/base-pistachio/lib/mk/core-pistachio.inc b/repos/base-pistachio/lib/mk/core-pistachio.inc
index e9267cb990..b685e1bf3f 100644
--- a/repos/base-pistachio/lib/mk/core-pistachio.inc
+++ b/repos/base-pistachio/lib/mk/core-pistachio.inc
@@ -1,6 +1,7 @@
-LIBS         = base-pistachio-common syscall-pistachio cxx
+LIBS = base-pistachio-common syscall-pistachio cxx
 
-GEN_CORE_DIR = $(BASE_DIR)/src/core
+GEN_CORE_DIR := $(dir $(call select_from_repositories,src/core/main.cc))
+GEN_SRC_DIR  := $(realpath $(GEN_CORE_DIR)/..)
 
 SRC_CC       = stack_area.cc \
                core_log.cc \
@@ -39,7 +40,7 @@ SRC_CC       = stack_area.cc \
                trace_session_component.cc
 
 INC_DIR     += $(REP_DIR)/src/core/include $(GEN_CORE_DIR)/include \
-               $(REP_DIR)/src/include      $(BASE_DIR)/src/include
+               $(REP_DIR)/src/include      $(GEN_SRC_DIR)/include
 
 include $(GEN_CORE_DIR)/version.inc
 
@@ -66,4 +67,3 @@ vpath core_rpc_cap_alloc.cc       $(GEN_CORE_DIR)
 vpath core_region_map.cc          $(GEN_CORE_DIR)
 vpath stack_area.cc               $(GEN_CORE_DIR)
 vpath pager_ep.cc                 $(GEN_CORE_DIR)
-vpath %.cc                        $(REP_DIR)/src/core
diff --git a/repos/base-pistachio/lib/mk/spec/x86_32/core-pistachio.mk b/repos/base-pistachio/lib/mk/spec/x86_32/core-pistachio.mk
index be5b43f4de..22c5b3ec29 100644
--- a/repos/base-pistachio/lib/mk/spec/x86_32/core-pistachio.mk
+++ b/repos/base-pistachio/lib/mk/spec/x86_32/core-pistachio.mk
@@ -8,3 +8,4 @@ vpath io_port_session_component.cc $(GEN_CORE_DIR)/spec/x86
 vpath io_port_session_support.cc   $(GEN_CORE_DIR)/spec/x86
 vpath platform_services.cc         $(GEN_CORE_DIR)/spec/x86
 vpath platform_x86.cc              $(REP_DIR)/src/core/spec/x86
+vpath %.cc                         $(REP_DIR)/src/core