diff --git a/core/main.mk b/core/main.mk
index f6dbd9d..97ed93d 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -41,7 +41,12 @@
 # without changing the command line every time.  Avoids rebuilds
 # when using ninja.
 $(shell mkdir -p $(SOONG_OUT_DIR) && \
-    echo -n $(BUILD_NUMBER) > $(SOONG_OUT_DIR)/build_number.txt)
+    echo -n $(BUILD_NUMBER) > $(SOONG_OUT_DIR)/build_number.tmp; \
+    if ! cmp -s $(SOONG_OUT_DIR)/build_number.tmp $(SOONG_OUT_DIR)/build_number.txt; then \
+        mv $(SOONG_OUT_DIR)/build_number.tmp $(SOONG_OUT_DIR)/build_number.txt; \
+    else \
+        rm $(SOONG_OUT_DIR)/build_number.tmp; \
+    fi)
 BUILD_NUMBER_FILE := $(SOONG_OUT_DIR)/build_number.txt
 .KATI_READONLY := BUILD_NUMBER_FILE
 $(KATI_obsolete_var BUILD_NUMBER,See https://android.googlesource.com/platform/build/+/master/Changes.md#BUILD_NUMBER)