diff --git a/src/main/kotlin/net/thauvin/erik/gradle/semver/SemverPlugin.kt b/src/main/kotlin/net/thauvin/erik/gradle/semver/SemverPlugin.kt
index 6f06651..a0341e5 100644
--- a/src/main/kotlin/net/thauvin/erik/gradle/semver/SemverPlugin.kt
+++ b/src/main/kotlin/net/thauvin/erik/gradle/semver/SemverPlugin.kt
@@ -47,20 +47,36 @@ class SemverPlugin : Plugin<Project> {
 
     companion object {
         fun saveProperties(config: SemverConfig, version: Version) {
+            val propsFile = File(config.properties)
             SortedProperties().apply {
+                propsFile.apply {
+                    if (canRead() && isFile) {
+                        FileInputStream(this).reader().use { load(it) }
+                    }
+                }
+
                 put(config.majorKey, version.major)
                 put(config.minorKey, version.minor)
                 put(config.patchKey, version.patch)
                 put(config.preReleaseKey, version.preRelease)
                 put(config.buildMetaKey, version.buildMeta)
-                if (version.buildMetaPrefix != Version.DEFAULT_BUILDMETA_PREFIX)
+                if (version.buildMetaPrefix != Version.DEFAULT_BUILDMETA_PREFIX
+                    || containsKey(config.buildMetaPrefixKey))
                     put(config.buildMetaPrefixKey, version.buildMetaPrefix)
-                if (version.preReleasePrefix != Version.DEFAULT_PRERELEASE_PREFIX)
+                if (version.preReleasePrefix != Version.DEFAULT_PRERELEASE_PREFIX
+                    || containsKey(config.preReleasePrefixKey))
                     put(config.preReleasePrefixKey, version.preReleasePrefix)
-                if (version.separator != Version.DEFAULT_SEPARATOR)
+                if (version.separator != Version.DEFAULT_SEPARATOR || containsKey(config.separatorKey))
                     put(config.separatorKey, version.separator)
-                FileOutputStream(config.properties).writer().use { writer ->
-                    store(writer, "Generated by the Semver Plugin for Gradle")
+
+                propsFile.apply {
+                    if (canWrite()) {
+                        FileOutputStream(this).writer().use {
+                            store(it, "Generated by the Semver Plugin for Gradle")
+                        }
+                    } else {
+                        throw GradleException("Unable to write version to: `$absoluteFile`")
+                    }
                 }
             }
         }