diff --git a/src/main/java/com/github/os72/protocjar/Protoc.java b/src/main/java/com/github/os72/protocjar/Protoc.java
index 754a674..a2b55f9 100644
--- a/src/main/java/com/github/os72/protocjar/Protoc.java
+++ b/src/main/java/com/github/os72/protocjar/Protoc.java
@@ -149,8 +149,7 @@ else if (file.getName().endsWith(".java")) {
 				FileInputStream is = null;
 				FileOutputStream os = null;
 				try {
-					if (version.length() <= 5) version = version.replace(".", ""); // "1.2.3" -> "123"
-					else version = "_" + version.replace(".", "_"); // "3.11.1" -> "_3_11_1"
+					version = javaShadingVersion(version);
 					tmpFile = File.createTempFile(file.getName(), null);
 					pw = new PrintWriter(tmpFile);
 					br = new BufferedReader(new FileReader(file));
@@ -177,6 +176,16 @@ else if (file.getName().endsWith(".java")) {
 		}
 	}
 
+	static String javaShadingVersion(String version) {
+		if (!version.contains(".")) {
+			return version;
+		} else if (version.length() <= 5) {
+			return version.replace(".", ""); // "1.2.3" -> "123"
+		} else {
+			return "_" + version.replace(".", "_");
+		}
+	}
+
 	public static File extractProtoc(ProtocVersion protocVersion, boolean includeStdTypes) throws IOException {
 		return extractProtoc(protocVersion, includeStdTypes, null);
 	}
diff --git a/src/test/java/com/github/os72/protocjar/ProtocTest.java b/src/test/java/com/github/os72/protocjar/ProtocTest.java
index 77feb12..b17eddd 100644
--- a/src/test/java/com/github/os72/protocjar/ProtocTest.java
+++ b/src/test/java/com/github/os72/protocjar/ProtocTest.java
@@ -15,10 +15,10 @@
  */
 package com.github.os72.protocjar;
 
-import java.io.File;
-
 import org.junit.Test;
 
+import java.io.File;
+
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
@@ -100,6 +100,15 @@ public void testRunProtocCompile() throws Exception {
 		}
 	}
 
+	@Test
+	public void testJavaShadingVersion() {
+		log("testJavaShadingVersion");
+		assertEquals("123", Protoc.javaShadingVersion("1.2.3"));
+		assertEquals("123", Protoc.javaShadingVersion("123"));
+		assertEquals("_3_11_1", Protoc.javaShadingVersion("3.11.1"));
+		assertEquals("_3_11_1", Protoc.javaShadingVersion("_3_11_1"));
+	}
+
 	@Test
 	public void testRunProtocCompileShade() throws Exception {
 		log("testRunProtocCompileShade");