diff --git a/core/Makefile b/core/Makefile
index 9cf539d..7911026 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -1261,19 +1261,23 @@
 recovery_wipe :=
 endif
 
-# Prior to A/B update, we used to have:
+# Traditionally with non-A/B OTA we have:
 #   boot.img + recovery-from-boot.p + recovery-resource.dat = recovery.img.
-# recovery-resource.dat is needed only if we carry a patch of the boot and
-# recovery images and invoke install-recovery.sh on the first boot post an
-# OTA update.
+# recovery-resource.dat is needed only if we carry an imgdiff patch of the boot and recovery images
+# and invoke install-recovery.sh on the first boot post an OTA update.
 #
 # We no longer need that if one of the following conditions holds:
-#   a) We carry a full copy of the recovery image
+#   a) We carry a full copy of the recovery image - no patching needed
 #      (BOARD_USES_FULL_RECOVERY_IMAGE = true);
-#   b) We build a single image that contains boot and recovery both
-#      (BOARD_USES_RECOVERY_AS_BOOT = true).
+#   b) We build a single image that contains boot and recovery both - no recovery image to install
+#      (BOARD_USES_RECOVERY_AS_BOOT = true);
+#   c) We build the root into system image - not needing the resource file as we do bsdiff
+#      (BOARD_BUILD_SYSTEM_ROOT_IMAGE = true).
+# Note that condition b) implies condition c), because of the earlier check in this file:
+# "BOARD_USES_RECOVERY_AS_BOOT = true must have BOARD_BUILD_SYSTEM_ROOT_IMAGE = true" (not vice
+# versa though).
 
-ifeq (,$(filter true, $(BOARD_USES_FULL_RECOVERY_IMAGE) $(BOARD_USES_RECOVERY_AS_BOOT)))
+ifeq (,$(filter true, $(BOARD_USES_FULL_RECOVERY_IMAGE) $(BOARD_BUILD_SYSTEM_ROOT_IMAGE)))
 # Named '.dat' so we don't attempt to use imgdiff for patching it.
 RECOVERY_RESOURCE_ZIP := $(TARGET_OUT)/etc/recovery-resource.dat
 else
@@ -1560,15 +1564,21 @@
 # image size check calculation.
 ifneq ($(INSTALLED_RECOVERYIMAGE_TARGET),)
 ifneq ($(BOARD_USES_FULL_RECOVERY_IMAGE),true)
+ifeq ($(BOARD_BUILD_SYSTEM_ROOT_IMAGE),true)
+diff_tool := $(HOST_OUT_EXECUTABLES)/bsdiff
+else
+diff_tool := $(HOST_OUT_EXECUTABLES)/imgdiff
+endif
 intermediates := $(call intermediates-dir-for,PACKAGING,recovery_patch)
 RECOVERY_FROM_BOOT_PATCH := $(intermediates)/recovery_from_boot.p
-$(RECOVERY_FROM_BOOT_PATCH): $(INSTALLED_RECOVERYIMAGE_TARGET) \
-                             $(INSTALLED_BOOTIMAGE_TARGET) \
-			     $(HOST_OUT_EXECUTABLES)/imgdiff \
-	                     $(HOST_OUT_EXECUTABLES)/bsdiff
+$(RECOVERY_FROM_BOOT_PATCH): PRIVATE_DIFF_TOOL := $(diff_tool)
+$(RECOVERY_FROM_BOOT_PATCH): \
+		$(INSTALLED_RECOVERYIMAGE_TARGET) \
+		$(INSTALLED_BOOTIMAGE_TARGET) \
+		$(diff_tool)
 	@echo "Construct recovery from boot"
 	mkdir -p $(dir $@)
-	PATH=$(HOST_OUT_EXECUTABLES):$$PATH $(HOST_OUT_EXECUTABLES)/imgdiff $(INSTALLED_BOOTIMAGE_TARGET) $(INSTALLED_RECOVERYIMAGE_TARGET) $@
+	$(PRIVATE_DIFF_TOOL) $(INSTALLED_BOOTIMAGE_TARGET) $(INSTALLED_RECOVERYIMAGE_TARGET) $@
 else # $(BOARD_USES_FULL_RECOVERY_IMAGE) == true
 RECOVERY_FROM_BOOT_PATCH := $(INSTALLED_RECOVERYIMAGE_TARGET)
 endif