diff --git a/cmd/sbox/sbox.go b/cmd/sbox/sbox.go
index 7057b33..65a34fd 100644
--- a/cmd/sbox/sbox.go
+++ b/cmd/sbox/sbox.go
@@ -36,6 +36,7 @@
 	outputRoot    string
 	keepOutDir    bool
 	depfileOut    string
+	inputHash     string
 )
 
 func init() {
@@ -51,6 +52,8 @@
 	flag.StringVar(&depfileOut, "depfile-out", "",
 		"file path of the depfile to generate. This value will replace '__SBOX_DEPFILE__' in the command and will be treated as an output but won't be added to __SBOX_OUT_FILES__")
 
+	flag.StringVar(&inputHash, "input-hash", "",
+		"This option is ignored. Typical usage is to supply a hash of the list of input names so that the module will be rebuilt if the list (and thus the hash) changes.")
 }
 
 func usageViolation(violation string) {
@@ -59,7 +62,7 @@
 	}
 
 	fmt.Fprintf(os.Stderr,
-		"Usage: sbox -c <commandToRun> --sandbox-path <sandboxPath> --output-root <outputRoot> [--depfile-out depFile] <outputFile> [<outputFile>...]\n"+
+		"Usage: sbox -c <commandToRun> --sandbox-path <sandboxPath> --output-root <outputRoot> [--depfile-out depFile] [--input-hash hash] <outputFile> [<outputFile>...]\n"+
 			"\n"+
 			"Deletes <outputRoot>,"+
 			"runs <commandToRun>,"+
diff --git a/genrule/genrule.go b/genrule/genrule.go
index a0008d3..fe877fe 100644
--- a/genrule/genrule.go
+++ b/genrule/genrule.go
@@ -26,6 +26,7 @@
 
 	"android/soong/android"
 	"android/soong/shared"
+	"crypto/sha256"
 	"path/filepath"
 )
 
@@ -309,6 +310,7 @@
 			addLocationLabel(out.Rel(), []string{filepath.Join("__SBOX_OUT_DIR__", out.Rel())})
 		}
 
+		referencedIn := false
 		referencedDepfile := false
 
 		rawCommand, err := android.ExpandNinjaEscaped(task.cmd, func(name string) (string, bool, error) {
@@ -333,6 +335,7 @@
 				}
 				return locationLabels[firstLabel][0], false, nil
 			case "in":
+				referencedIn = true
 				return "${in}", true, nil
 			case "out":
 				return "__SBOX_OUT_FILES__", false, nil
@@ -398,8 +401,16 @@
 		// Escape the command for the shell
 		rawCommand = "'" + strings.Replace(rawCommand, "'", `'\''`, -1) + "'"
 		g.rawCommands = append(g.rawCommands, rawCommand)
-		sandboxCommand := fmt.Sprintf("rm -rf %s && $sboxCmd --sandbox-path %s --output-root %s -c %s %s $allouts",
-			task.genDir, sandboxPath, task.genDir, rawCommand, depfilePlaceholder)
+
+		sandboxCommand := fmt.Sprintf("rm -rf %s && $sboxCmd --sandbox-path %s --output-root %s",
+			task.genDir, sandboxPath, task.genDir)
+
+		if !referencedIn {
+			sandboxCommand = sandboxCommand + hashSrcFiles(srcFiles)
+		}
+
+		sandboxCommand = sandboxCommand + fmt.Sprintf(" -c %s %s $allouts",
+			rawCommand, depfilePlaceholder)
 
 		ruleParams := blueprint.RuleParams{
 			Command:     sandboxCommand,
@@ -463,6 +474,14 @@
 
 }
 
+func hashSrcFiles(srcFiles android.Paths) string {
+	h := sha256.New()
+	for _, src := range srcFiles {
+		h.Write([]byte(src.String()))
+	}
+	return fmt.Sprintf(" --input-hash %x", h.Sum(nil))
+}
+
 func (g *Module) generateSourceFile(ctx android.ModuleContext, task generateTask, rule blueprint.Rule) {
 	desc := "generate"
 	if len(task.out) == 0 {
diff --git a/genrule/genrule_test.go b/genrule/genrule_test.go
index 7eb43ac..4b36600 100644
--- a/genrule/genrule_test.go
+++ b/genrule/genrule_test.go
@@ -502,6 +502,93 @@
 	}
 }
 
+func TestGenruleHashInputs(t *testing.T) {
+
+	// The basic idea here is to verify that the sbox command (which is
+	// in the Command field of the generate rule) contains a hash of the
+	// inputs, but only if $(in) is not referenced in the genrule cmd
+	// property.
+
+	// By including a hash of the inputs, we cause the rule to re-run if
+	// the list of inputs changes (because the sbox command changes).
+
+	// However, if the genrule cmd property already contains $(in), then
+	// the dependency is already expressed, so we don't need to include the
+	// hash in that case.
+
+	bp := `
+			genrule {
+				name: "hash0",
+				srcs: ["in1.txt", "in2.txt"],
+				out: ["out"],
+				cmd: "echo foo > $(out)",
+			}
+			genrule {
+				name: "hash1",
+				srcs: ["*.txt"],
+				out: ["out"],
+				cmd: "echo bar > $(out)",
+			}
+			genrule {
+				name: "hash2",
+				srcs: ["*.txt"],
+				out: ["out"],
+				cmd: "echo $(in) > $(out)",
+			}
+		`
+	testcases := []struct {
+		name         string
+		expectedHash string
+	}{
+		{
+			name: "hash0",
+			// sha256 value obtained from: echo -n 'in1.txtin2.txt' | sha256sum
+			expectedHash: "031097e11e0a8c822c960eb9742474f46336360a515744000d086d94335a9cb9",
+		},
+		{
+			name: "hash1",
+			// sha256 value obtained from: echo -n 'in1.txtin2.txtin3.txt' | sha256sum
+			expectedHash: "de5d22a4a7ab50d250cc59fcdf7a7e0775790d270bfca3a7a9e1f18a70dd996c",
+		},
+		{
+			name: "hash2",
+			// $(in) is present, option should not appear
+			expectedHash: "",
+		},
+	}
+
+	config := testConfig(bp, nil)
+	ctx := testContext(config)
+	_, errs := ctx.ParseFileList(".", []string{"Android.bp"})
+	if errs == nil {
+		_, errs = ctx.PrepareBuildActions(config)
+	}
+	if errs != nil {
+		t.Fatal(errs)
+	}
+
+	for _, test := range testcases {
+		t.Run(test.name, func(t *testing.T) {
+			gen := ctx.ModuleForTests(test.name, "")
+			command := gen.Rule("generator").RuleParams.Command
+
+			if len(test.expectedHash) > 0 {
+				// We add spaces before and after to make sure that
+				// this option doesn't abutt another sbox option.
+				expectedInputHashOption := " --input-hash " + test.expectedHash + " "
+
+				if !strings.Contains(command, expectedInputHashOption) {
+					t.Errorf("Expected command \"%s\" to contain \"%s\"", command, expectedInputHashOption)
+				}
+			} else {
+				if strings.Contains(command, "--input-hash") {
+					t.Errorf("Unexpected \"--input-hash\" found in command: \"%s\"", command)
+				}
+			}
+		})
+	}
+}
+
 func TestGenSrcs(t *testing.T) {
 	testcases := []struct {
 		name string