diff --git a/open-java-format/src/main/java/com/palantir/javaformat/java/JavaCommentsHelper.java b/open-java-format/src/main/java/com/palantir/javaformat/java/JavaCommentsHelper.java
index a31fb7c25..83996c93d 100644
--- a/open-java-format/src/main/java/com/palantir/javaformat/java/JavaCommentsHelper.java
+++ b/open-java-format/src/main/java/com/palantir/javaformat/java/JavaCommentsHelper.java
@@ -167,10 +167,12 @@ private static boolean isJBangDirective(String text) {
         return matcher.lookingAt() && (matcher.group(1) != null || JBANG_DIRECTIVE_NAMES.contains(matcher.group(2)));
     }
 
+    private static final Pattern LINE_COMMENT_MISSING_SPACE_PREFIX = Pattern.compile("^(//+)[^\\s/]");
+
     // Preserve special `//noinspection` and `//$NON-NLS-x$` comments used by IDEs, which cannot
     // contain leading spaces.
-    private static final Pattern LINE_COMMENT_MISSING_SPACE_PREFIX =
-            Pattern.compile("^(//+)(?!noinspection|\\$NON-NLS-\\d+\\$)[^\\s/]");
+    private static final Pattern LINE_COMMENT_NO_SPACE_PREFIX =
+            Pattern.compile("^//+(noinspection|\\$NON-NLS-\\d+\\$)");
 
     private static String lineCommentPrefix(String line) {
         int prefixLength = 0;
@@ -191,7 +193,7 @@ private List<String> wrapLineComments(List<String> lines, int column0) {
             line = CharMatcher.whitespace().trimLeadingFrom(line);
             // Add missing leading spaces to line comments: `//foo` -> `// foo`.
             Matcher matcher = LINE_COMMENT_MISSING_SPACE_PREFIX.matcher(line);
-            if (matcher.find()) {
+            if (matcher.find() && !LINE_COMMENT_NO_SPACE_PREFIX.matcher(line).find()) {
                 int length = matcher.group(1).length();
                 line = "/".repeat(length) + " " + line.substring(length);
             }
diff --git a/open-java-format/src/test/java/com/palantir/javaformat/java/FormatterTest.java b/open-java-format/src/test/java/com/palantir/javaformat/java/FormatterTest.java
index 46be7a302..8a773d9b6 100644
--- a/open-java-format/src/test/java/com/palantir/javaformat/java/FormatterTest.java
+++ b/open-java-format/src/test/java/com/palantir/javaformat/java/FormatterTest.java
@@ -368,6 +368,33 @@ void onlyWrapLineCommentOnWhitespace_noLeadingWhitespace() throws Exception {
                         + "}\n");
     }
 
+    @Test
+    void lineCommentGetsItsMissingSpaceExceptIdeMarkers() throws Exception {
+        // `//foo` gets a space after any number of slashes, while the IDE markers `//noinspection` and `//$NON-NLS-n$`
+        // are recognised by their tools only without one and stay as written.
+        String input = "class T {\n"
+                + "  //noinspection unchecked\n"
+                + "  //$NON-NLS-1$ //$NON-NLS-2$\n"
+                + "  //$NON-NLS-12$ and more\n"
+                + "  //foo\n"
+                + "  ///foo\n"
+                + "  // bar\n"
+                + "  //  two spaces\n"
+                + "  void m() {}\n"
+                + "}\n";
+        String expected = "class T {\n"
+                + "  //noinspection unchecked\n"
+                + "  //$NON-NLS-1$ //$NON-NLS-2$\n"
+                + "  //$NON-NLS-12$ and more\n"
+                + "  // foo\n"
+                + "  /// foo\n"
+                + "  // bar\n"
+                + "  //  two spaces\n"
+                + "  void m() {}\n"
+                + "}\n";
+        assertThat(Formatter.create().formatSource(input)).isEqualTo(expected);
+    }
+
     @Test
     void throwsFormatterException() throws Exception {
         assertThatThrownBy(() -> Formatter.create().formatSourceAndFixImports("package foo; public class {"))