diff --git a/core/Makefile b/core/Makefile
index c03f21f..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
@@ -2781,9 +2791,15 @@
 	$(hide) $(call fs_config,$(zip_root)/PRODUCT,product/) > $(zip_root)/META/product_filesystem_config.txt
 endif
 ifeq ($(BOARD_BUILD_SYSTEM_ROOT_IMAGE),true)
+	@# When using BOARD_BUILD_SYSTEM_ROOT_IMAGE, ROOT always contains the files for the root under
+	@# normal boot. BOOT/RAMDISK exists only if additionally using BOARD_USES_RECOVERY_AS_BOOT.
 	$(hide) $(call fs_config,$(zip_root)/ROOT,) > $(zip_root)/META/root_filesystem_config.txt
-endif
+ifeq ($(BOARD_USES_RECOVERY_AS_BOOT),true)
 	$(hide) $(call fs_config,$(zip_root)/BOOT/RAMDISK,) > $(zip_root)/META/boot_filesystem_config.txt
+endif
+else # BOARD_BUILD_SYSTEM_ROOT_IMAGE != true
+	$(hide) $(call fs_config,$(zip_root)/BOOT/RAMDISK,) > $(zip_root)/META/boot_filesystem_config.txt
+endif
 ifneq ($(INSTALLED_RECOVERYIMAGE_TARGET),)
 	$(hide) $(call fs_config,$(zip_root)/RECOVERY/RAMDISK,) > $(zip_root)/META/recovery_filesystem_config.txt
 endif
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index 743c6a0..787de98 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -1828,35 +1828,47 @@
 
 def MakeRecoveryPatch(input_dir, output_sink, recovery_img, boot_img,
                       info_dict=None):
-  """Generate a binary patch that creates the recovery image starting
-  with the boot image.  (Most of the space in these images is just the
-  kernel, which is identical for the two, so the resulting patch
-  should be efficient.)  Add it to the output zip, along with a shell
-  script that is run from init.rc on first boot to actually do the
-  patching and install the new recovery image.
+  """Generates the recovery-from-boot patch and writes the script to output.
 
-  recovery_img and boot_img should be File objects for the
-  corresponding images.  info should be the dictionary returned by
-  common.LoadInfoDict() on the input target_files.
+  Most of the space in the boot and recovery images is just the kernel, which is
+  identical for the two, so the resulting patch should be efficient. Add it to
+  the output zip, along with a shell script that is run from init.rc on first
+  boot to actually do the patching and install the new recovery image.
+
+  Args:
+    input_dir: The top-level input directory of the target-files.zip.
+    output_sink: The callback function that writes the result.
+    recovery_img: File object for the recovery image.
+    boot_img: File objects for the boot image.
+    info_dict: A dict returned by common.LoadInfoDict() on the input
+        target_files. Will use OPTIONS.info_dict if None has been given.
   """
-
   if info_dict is None:
     info_dict = OPTIONS.info_dict
 
-  full_recovery_image = info_dict.get("full_recovery_image", None) == "true"
+  full_recovery_image = info_dict.get("full_recovery_image") == "true"
 
   if full_recovery_image:
     output_sink("etc/recovery.img", recovery_img.data)
 
   else:
-    diff_program = ["imgdiff"]
+    system_root_image = info_dict.get("system_root_image") == "true"
     path = os.path.join(input_dir, "SYSTEM", "etc", "recovery-resource.dat")
-    if os.path.exists(path):
-      diff_program.append("-b")
-      diff_program.append(path)
-      bonus_args = "-b /system/etc/recovery-resource.dat"
-    else:
+    # With system-root-image, boot and recovery images will have mismatching
+    # entries (only recovery has the ramdisk entry) (Bug: 72731506). Use bsdiff
+    # to handle such a case.
+    if system_root_image:
+      diff_program = ["bsdiff"]
       bonus_args = ""
+      assert not os.path.exists(path)
+    else:
+      diff_program = ["imgdiff"]
+      if os.path.exists(path):
+        diff_program.append("-b")
+        diff_program.append(path)
+        bonus_args = "-b /system/etc/recovery-resource.dat"
+      else:
+        bonus_args = ""
 
     d = Difference(recovery_img, boot_img, diff_program=diff_program)
     _, _, patch = d.ComputePatch()