diff --git a/src/main/java/com/github/hexomod/macro/Preprocessor.java b/src/main/java/com/github/hexomod/macro/Preprocessor.java
index e1d2e12..0383257 100644
--- a/src/main/java/com/github/hexomod/macro/Preprocessor.java
+++ b/src/main/java/com/github/hexomod/macro/Preprocessor.java
@@ -242,7 +242,7 @@ String commentLine(String line, Map<String, String> keywords) {
         if (trimLine.startsWith(keywords.get("comment"))) {
             return line;
         } else {
-            return StringUtils.repeat(" ", indent) + keywords.get("comment") + " " + trimLine;
+            return line.substring(0, indent) + keywords.get("comment") + " " + trimLine;
         }
     }
 
@@ -250,7 +250,7 @@ String uncommentLine(String line, Map<String, String> keywords) {
         int indent = getIndentSize(line);
         String trimLine = line.trim();
         if (trimLine.startsWith(keywords.get("comment"))) {
-            return StringUtils.repeat(" ", indent) + trimLine.substring(keywords.get("comment").length()).trim();
+            return line.substring(0, indent) + trimLine.substring(keywords.get("comment").length()).trim();
         } else {
             return line;
         }
diff --git a/src/test/java/com/github/hexomod/macro/PreprocessorTest.java b/src/test/java/com/github/hexomod/macro/PreprocessorTest.java
index bc0fb62..34a8a99 100644
--- a/src/test/java/com/github/hexomod/macro/PreprocessorTest.java
+++ b/src/test/java/com/github/hexomod/macro/PreprocessorTest.java
@@ -23,13 +23,18 @@
  */
 package com.github.hexomod.macro;
 
+import org.junit.BeforeClass;
 import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
 
-import java.util.ArrayList;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.*;
+import java.util.stream.Collectors;
 
+import static com.github.hexomod.macro.Preprocessor.HASH_KEYWORDS;
 import static com.github.hexomod.macro.Preprocessor.SLASH_KEYWORDS;
 import static org.junit.Assert.*;
 
@@ -440,4 +445,50 @@ public void processLines_simple_ifdef_elseif_t_f_f() {
         assertTrue(lines.get(4).compareTo(preprocessor.commentLine(testLine1, SLASH_KEYWORDS))==0);
         assertTrue(lines.get(6).compareTo(preprocessor.commentLine(testLine, SLASH_KEYWORDS))==0);
     }
-}
\ No newline at end of file
+
+	@RunWith(Parameterized.class)
+	public static class CommentTests {
+		static Preprocessor preprocessor;
+		@BeforeClass
+		public static void setup() {
+			preprocessor = new Preprocessor(Collections.emptyMap());
+		}
+
+		@Parameterized.Parameter(0) public String plain;
+		@Parameterized.Parameter(1) public String commented;
+		@Parameterized.Parameter(2) public Map<String, String> keywords;
+		@Parameterized.Parameters
+		public static Collection<Object[]> data() {
+			try {
+				BufferedReader reader = new BufferedReader(
+						new InputStreamReader(PreprocessorTest.class.getResource("preprocessor_comment_data.csv").openStream())
+				);
+				List<Object[]> data = reader.lines().map(line -> {
+					String[] parts = line.split("\\|");
+					if ("SLASH".equals(parts[2])) {
+						return new Object[]{parts[0], parts[1], SLASH_KEYWORDS};
+					} else if ("HASH".equals(parts[2])) {
+						return new Object[]{parts[0], parts[1], HASH_KEYWORDS};
+					} else {
+						throw new RuntimeException();
+					}
+				}).collect(Collectors.toList());
+
+				reader.close();
+				return data;
+			} catch (IOException e) {
+				throw new RuntimeException(e);
+			}
+		}
+
+		@Test
+		public void commentLine() {
+			assertEquals("Trying to comment \"" + plain + "\"", commented, preprocessor.commentLine(plain, keywords));
+		}
+
+		@Test
+		public void uncommentLine() {
+			assertEquals("Trying to uncomment \"" + commented + "\"", plain, preprocessor.uncommentLine(commented, keywords));
+		}
+	}
+}
diff --git a/src/test/resources/com/github/hexomod/macro/preprocessor_comment_data.csv b/src/test/resources/com/github/hexomod/macro/preprocessor_comment_data.csv
new file mode 100644
index 0000000..b947ea3
--- /dev/null
+++ b/src/test/resources/com/github/hexomod/macro/preprocessor_comment_data.csv
@@ -0,0 +1,14 @@
+String message = "0";|/// String message = "0";|SLASH
+String message = "1";|### String message = "1";|HASH
+	String message = "2";|	/// String message = "2";|SLASH
+	String message = "3";|	### String message = "3";|HASH
+  String message = "4";|  /// String message = "4";|SLASH
+  String message = "5";|  ### String message = "5";|HASH
+    String message = "6";|    /// String message = "6";|SLASH
+    String message = "7";|    ### String message = "7";|HASH
+	  String message = "8";|	  /// String message = "8";|SLASH
+	  String message = "9";|	  ### String message = "9";|HASH
+// comment|/// // comment|SLASH
+# comment|### # comment|HASH
+	// comment|	/// // comment|SLASH
+	# comment|	### # comment|HASH