diff --git a/hooks/check-diff.py b/hooks/check-diff.py
index 36f5b69..d2dc140 100755
--- a/hooks/check-diff.py
+++ b/hooks/check-diff.py
@@ -3,6 +3,7 @@
 import re, sys
 
 PAT_TAB = re.compile("#?\t*[^\t]*$")
+PAT_BAD_COMMENT = re.compile(r"\s*//")
 
 def checkascii(l):
   return any((ord(c) < 32 or ord(c) > 127) and c != '\t' for c in l)
@@ -45,6 +46,9 @@ def checkascii(l):
     if is_source and l.startswith("  "):
       sys.stderr.write("*** {}:{}: Use tabs for indentation: '{}'\n".format(filename, line, l))
       status = 1
+    if is_source and PAT_BAD_COMMENT.match(l):
+      sys.stderr.write("*** {}:{}: Use /* */ for free standing comments: '{}'\n".format(filename, line, l))
+      status = 1
     line += 1
   elif l.startswith(" "):
     line += 1
diff --git a/test/cases/case8.cpp b/test/cases/case8.cpp
new file mode 100644
index 0000000..2ff60ae
--- /dev/null
+++ b/test/cases/case8.cpp
@@ -0,0 +1,7 @@
+// Foo
+// bar
+
+int foo()
+{
+	return bar;
+}
diff --git a/test/cases/case9.cpp b/test/cases/case9.cpp
new file mode 100644
index 0000000..783a668
--- /dev/null
+++ b/test/cases/case9.cpp
@@ -0,0 +1,7 @@
+	// Foo
+	// bar
+
+int foo()
+{
+	return bar;
+}
diff --git a/test/test.sh b/test/test.sh
index ede5ea4..815c7a0 100755
--- a/test/test.sh
+++ b/test/test.sh
@@ -163,6 +163,14 @@ git_good add case7.cpp
 test_commit_bad "Add: Preprocessor hash indented"
 git_good reset case7.cpp
 
+git_good add case8.cpp
+test_commit_bad "Add: Wrong comment style"
+git_good reset case8.cpp
+
+git_good add case9.cpp
+test_commit_bad "Add: Wrong comment style"
+git_good reset case9.cpp
+
 git_good push
 
 # setup badguy