diff --git a/install_process.go b/install_process.go
index 89ae741e..558a8344 100644
--- a/install_process.go
+++ b/install_process.go
@@ -78,7 +78,7 @@ func (ip YarnInstallProcess) ShouldRun(workingDir string, metadata map[string]in
 		return true, "", fmt.Errorf("failed to write temp file for %s: %w", file.Name(), err)
 	}
 
-	sum, err := ip.summer.Sum(filepath.Join(workingDir, "yarn.lock"), file.Name())
+	sum, err := ip.summer.Sum(filepath.Join(workingDir, "yarn.lock"), filepath.Join(workingDir, "package.json"), file.Name())
 	if err != nil {
 		return true, "", fmt.Errorf("unable to sum config files: %w", err)
 	}
diff --git a/install_process_test.go b/install_process_test.go
index ab0e92b4..4d68b7e6 100644
--- a/install_process_test.go
+++ b/install_process_test.go
@@ -79,7 +79,8 @@ func testInstallProcess(t *testing.T, context spec.G, it spec.S) {
 						"cache_sha": "some-sha",
 					})
 					Expect(summer.SumCall.Receives.Paths[0]).To(Equal(filepath.Join(workingDir, "yarn.lock")))
-					Expect(summer.SumCall.Receives.Paths[1]).To(ContainSubstring("config-file"))
+					Expect(summer.SumCall.Receives.Paths[1]).To(Equal(filepath.Join(workingDir, "package.json")))
+					Expect(summer.SumCall.Receives.Paths[2]).To(ContainSubstring("config-file"))
 					Expect(run).To(BeTrue())
 					Expect(sha).To(Equal("some-other-sha"))
 					Expect(err).NotTo(HaveOccurred())