diff --git a/ui/build/build.go b/ui/build/build.go
index 95d7831..781ca18 100644
--- a/ui/build/build.go
+++ b/ui/build/build.go
@@ -401,6 +401,7 @@
 		if what&RunKati != 0 {
 			installCleanIfNecessary(ctx, config)
 		}
+		partialCompileCleanIfNecessary(ctx, config)
 		runNinjaForBuild(ctx, config)
 		updateBuildIdDir(ctx, config)
 	}
diff --git a/ui/build/cleanbuild.go b/ui/build/cleanbuild.go
index 41cb5ab..723d90f 100644
--- a/ui/build/cleanbuild.go
+++ b/ui/build/cleanbuild.go
@@ -218,6 +218,52 @@
 	writeConfig()
 }
 
+// When SOONG_USE_PARTIAL_COMPILE transitions from on to off, we need to remove
+// all files which were potentially built with partial compile, so that they
+// get rebuilt with that turned off.
+func partialCompileCleanIfNecessary(ctx Context, config Config) {
+	configFile := config.DevicePreviousUsePartialCompile()
+	currentValue, _ := config.Environment().Get("SOONG_USE_PARTIAL_COMPILE")
+
+	ensureDirectoriesExist(ctx, filepath.Dir(configFile))
+
+	writeValue := func() {
+		err := ioutil.WriteFile(configFile, []byte(currentValue), 0666) // a+rw
+		if err != nil {
+			ctx.Fatalln("Failed to write use partial compile config:", err)
+		}
+	}
+
+	previousValueBytes, err := ioutil.ReadFile(configFile)
+	if err != nil {
+		if os.IsNotExist(err) {
+			// Just write the new config file, no old config file to worry about.
+			writeValue()
+			return
+		} else {
+			ctx.Fatalln("Failed to read previous use partial compile config:", err)
+		}
+	}
+
+	previousValue := string(previousValueBytes)
+	switch previousValue {
+	case currentValue:
+		// Same value as before - nothing left to do here.
+		return
+	case "true":
+		// Transitioning from on to off.  Build (phony) target: partialcompileclean.
+		ctx.BeginTrace(metrics.PrimaryNinja, "partialcompileclean")
+		defer ctx.EndTrace()
+
+		ctx.Printf("SOONG_USE_PARTIAL_COMPILE turned off, forcing partialcompileclean\n")
+
+		runNinja(ctx, config, []string{"partialcompileclean"})
+	default:
+		// Transitioning from off to on.  Nothing to do in this case.
+	}
+	writeValue()
+}
+
 // cleanOldFiles takes an input file (with all paths relative to basePath), and removes files from
 // the filesystem if they were removed from the input file since the last execution.
 func cleanOldFiles(ctx Context, basePath, newFile string) {
diff --git a/ui/build/config.go b/ui/build/config.go
index 2a00c41..a4f778d 100644
--- a/ui/build/config.go
+++ b/ui/build/config.go
@@ -1685,6 +1685,10 @@
 	return filepath.Join(c.ProductOut(), "previous_build_config.mk")
 }
 
+func (c *configImpl) DevicePreviousUsePartialCompile() string {
+	return filepath.Join(c.ProductOut(), "previous_use_partial_compile.txt")
+}
+
 func (c *configImpl) KatiPackageMkDir() string {
 	return filepath.Join(c.SoongOutDir(), "kati_packaging"+c.KatiSuffix())
 }
diff --git a/ui/build/ninja.go b/ui/build/ninja.go
index 1d4285f..e2a568f 100644
--- a/ui/build/ninja.go
+++ b/ui/build/ninja.go
@@ -36,10 +36,16 @@
 	ninjaWeightListFileName = ".ninja_weight_list"
 )
 
+// Runs ninja with the arguments from the command line, as found in
+// config.NinjaArgs().
+func runNinjaForBuild(ctx Context, config Config) {
+	runNinja(ctx, config, config.NinjaArgs())
+}
+
 // Constructs and runs the Ninja command line with a restricted set of
 // environment variables. It's important to restrict the environment Ninja runs
 // for hermeticity reasons, and to avoid spurious rebuilds.
-func runNinjaForBuild(ctx Context, config Config) {
+func runNinja(ctx Context, config Config, ninjaArgs []string) {
 	ctx.BeginTrace(metrics.PrimaryNinja, "ninja")
 	defer ctx.EndTrace()
 
@@ -88,7 +94,7 @@
 			"-w", "missingdepfile=err",
 		}
 	}
-	args = append(args, config.NinjaArgs()...)
+	args = append(args, ninjaArgs...)
 
 	var parallel int
 	if config.UseRemoteBuild() {
@@ -244,6 +250,8 @@
 			"RUST_LOG",
 
 			// SOONG_USE_PARTIAL_COMPILE only determines which half of the rule we execute.
+			// When it transitions true => false, we build phony target "partialcompileclean",
+			// which removes all files that could have been created while it was true.
 			"SOONG_USE_PARTIAL_COMPILE",
 
 			// Directory for ExecutionMetrics