diff --git a/core/binary.mk b/core/binary.mk
index 73d1d22..be6107c 100644
--- a/core/binary.mk
+++ b/core/binary.mk
@@ -733,24 +733,20 @@
 aidl_gen_cpp :=
 ifneq ($(aidl_src),)
 
+# Use the intermediates directory to avoid writing our own .cpp -> .o rules.
 aidl_gen_cpp_root := $(intermediates)/aidl-generated/src
 aidl_gen_include_root := $(intermediates)/aidl-generated/include
 
-aidl_gen_cpp := $(patsubst %.aidl,%$(LOCAL_CPP_EXTENSION),$(aidl_src))
-aidl_gen_cpp := $(addprefix $(aidl_gen_cpp_root)/,$(aidl_gen_cpp))
+# Multi-architecture builds have distinct intermediates directories.
+# Thus we'll actually generate source for each architecture.
+$(foreach s,$(aidl_src),\
+    $(eval $(call define-aidl-cpp-rule,$(s),$(aidl_gen_cpp_root),aidl_gen_cpp)))
+-include $(addsuffix .P,$(basename $(aidl_gen_cpp)))
 
-# TODO(wiley): we could pass down a flag here to only generate the server or
-#              client side of the binder interface.
 $(aidl_gen_cpp) : PRIVATE_MODULE := $(LOCAL_MODULE)
 $(aidl_gen_cpp) : PRIVATE_HEADER_OUTPUT_DIR := $(aidl_gen_include_root)
 $(aidl_gen_cpp) : PRIVATE_AIDL_FLAGS := $(addprefix -I,$(LOCAL_AIDL_INCLUDES))
 
-# Multi-architecture builds have distinct intermediates directories.
-# Define rules for both architectures.
-$(aidl_gen_cpp) : $(aidl_gen_cpp_root)/%$(LOCAL_CPP_EXTENSION) : $(LOCAL_PATH)/%.aidl $(AIDL_CPP)
-	$(transform-aidl-to-cpp)
--include $(addsuffix .P,$(basename $(aidl_gen_cpp)))
-
 # Add generated headers to include paths.
 my_c_includes += $(aidl_gen_include_root)
 my_export_c_include_dirs += $(aidl_gen_include_root)
diff --git a/core/definitions.mk b/core/definitions.mk
index 623f209..4b820de 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -993,6 +993,18 @@
     $< $(PRIVATE_HEADER_OUTPUT_DIR) $@
 endef
 
+## Given a .aidl file path generate the rule to compile it a .cpp file.
+# $(1): a .aidl source file
+# $(2): a directory to place the generated .cpp files in
+# $(3): name of a variable to add the path to the generated source file to
+#
+# You must call this with $(eval).
+define define-aidl-cpp-rule
+define-aidl-cpp-rule-src := $(patsubst %.aidl,%$(LOCAL_CPP_EXTENSION),$(subst ../,dotdot/,$(addprefix $(2)/,$(1))))
+$$(define-aidl-cpp-rule-src) : $(LOCAL_PATH)/$(1) $(AIDL_CPP)
+	$$(transform-aidl-to-cpp)
+$(3) += $$(define-aidl-cpp-rule-src)
+endef
 
 ###########################################################
 ## Commands for running java-event-log-tags.py