diff --git a/cpp/ql/src/Documentation/CommentedOutCode.qll b/cpp/ql/src/Documentation/CommentedOutCode.qll
index 5bb22623564..9155e1613a5 100644
--- a/cpp/ql/src/Documentation/CommentedOutCode.qll
+++ b/cpp/ql/src/Documentation/CommentedOutCode.qll
@@ -47,12 +47,27 @@ private predicate looksLikeCode(string line) {
   )
 }
 
+/**
+ * Holds if there is a preprocessor directive on the line indicated by
+ * `f` and `line`.
+ */
+private predicate preprocLine(File f, int line) {
+  exists(PreprocessorDirective pd, Location l |
+    pd.getLocation() = l and
+    l.getFile() = f and
+    l.getStartLine() = line
+  )
+}
+
 /**
  * The line of a C++-style comment within its file `f`.
  */
 private int lineInFile(CppStyleComment c, File f) {
   f = c.getFile() and
-  result = c.getLocation().getStartLine()
+  result = c.getLocation().getStartLine() and
+
+  // Ignore comments on the same line as a preprocessor directive.
+  not preprocLine(f, result)
 }
 
 /**
@@ -89,9 +104,17 @@ private int commentId(CppStyleComment c, File f, int line) {
  */
 class CommentBlock extends Comment {
   CommentBlock() {
-    this instanceof CppStyleComment
-    implies
-    not exists(CppStyleComment pred, File f | lineInFile(pred, f) + 1 = lineInFile(this, f))
+  	(
+      this instanceof CppStyleComment
+      implies
+      not exists(CppStyleComment pred, File f | lineInFile(pred, f) + 1 = lineInFile(this, f))
+    ) and (
+      // Ignore comments on the same line as a preprocessor directive.
+      not exists(Location l |
+        l = this.getLocation() and
+        preprocLine(l.getFile(), l.getStartLine())
+      )
+    )
   }
 
   /**
diff --git a/cpp/ql/test/query-tests/Documentation/CommentedOutCode/CommentedOutCode.expected b/cpp/ql/test/query-tests/Documentation/CommentedOutCode/CommentedOutCode.expected
index 1280bd0b3c7..a406bf53f8d 100644
--- a/cpp/ql/test/query-tests/Documentation/CommentedOutCode/CommentedOutCode.expected
+++ b/cpp/ql/test/query-tests/Documentation/CommentedOutCode/CommentedOutCode.expected
@@ -11,12 +11,7 @@
 | test2.cpp:63:1:63:15 | // #pragma once | This comment appears to contain commented-out code |
 | test2.cpp:65:1:65:17 | //  # pragma once | This comment appears to contain commented-out code |
 | test2.cpp:67:1:67:19 | /*#error"myerror"*/ | This comment appears to contain commented-out code |
-| test2.cpp:73:8:73:24 | // #ifdef MYMACRO | This comment appears to contain commented-out code |
-| test2.cpp:79:7:79:30 | // #if !defined(MYMACRO) | This comment appears to contain commented-out code |
-| test2.cpp:83:8:83:37 | // #else #if !defined(MYMACRO) | This comment appears to contain commented-out code |
-| test2.cpp:89:10:89:45 | //    #ifdef MYMACRO       (comment) | This comment appears to contain commented-out code |
 | test2.cpp:91:1:95:2 | /*\n#ifdef MYMACRO\n\t// ...\n#endif // #ifdef MYMACRO\n*/ | This comment appears to contain commented-out code |
-| test2.cpp:103:3:105:25 | // comment at end of block | This comment appears to contain commented-out code |
 | test.c:2:1:2:22 | // commented out code; | This comment appears to contain commented-out code |
 | test.c:4:1:7:8 | // some; | This comment appears to contain commented-out code |
 | test.c:9:1:13:8 | // also; | This comment appears to contain commented-out code |