diff --git a/common/t-iobuf.c b/common/t-iobuf.c
index 01c94a380..ae72fde90 100644
--- a/common/t-iobuf.c
+++ b/common/t-iobuf.c
@@ -27,7 +27,7 @@ every_other_filter (void *opaque, int control,
       else
 	c2 = iobuf_readbyte (chain);
 
-      // printf ("Discarding %d (%c); return %d (%c)\n", c, c, c2, c2);
+      /* printf ("Discarding %d (%c); return %d (%c)\n", c, c, c2, c2); */
 
       if (c2 == -1)
 	{
@@ -149,12 +149,12 @@ main (int argc, char *argv[])
     n = 0;
     while ((c = iobuf_readbyte (iobuf)) != -1)
       {
-	// printf ("%d: %c\n", n + 1, (char) c);
+	/* printf ("%d: %c\n", n + 1, (char) c); */
 	assert (content[2 * n + 1] == c);
 	n ++;
       }
-    // printf ("Got EOF after reading %d bytes (content: %d)\n",
-    // n, strlen (content));
+    /* printf ("Got EOF after reading %d bytes (content: %d)\n", */
+    /*         n, strlen (content)); */
     assert (n == strlen (content) / 2);
 
     iobuf_close (iobuf);
@@ -185,7 +185,7 @@ main (int argc, char *argv[])
 
     while ((c = iobuf_readbyte (iobuf)) != -1)
       {
-	// printf ("%d: %c\n", n + 1, (char) c);
+	/* printf ("%d: %c\n", n + 1, (char) c); */
 	assert (content[2 * (n - 5) + 1] == c);
 	n ++;
       }
@@ -293,7 +293,7 @@ main (int argc, char *argv[])
 	c = iobuf_readbyte (iobuf);
 	if (c == -1 && lastc == -1)
 	  {
-	    // printf("Two EOFs in a row.  Done.\n");
+	    /* printf("Two EOFs in a row.  Done.\n");  */
 	    assert (n == 44);
 	    break;
 	  }
@@ -302,13 +302,13 @@ main (int argc, char *argv[])
 
 	if (c == -1)
 	  {
-	    // printf("After %d bytes, got EOF.\n", n);
+	    /* printf("After %d bytes, got EOF.\n", n); */
 	    assert (n == 27 || n == 44);
 	  }
 	else
 	  {
 	    n ++;
-	    // printf ("%d: '%c' (%d)\n", n, c, c);
+	    /* printf ("%d: '%c' (%d)\n", n, c, c); */
 	  }
       }
   }
@@ -366,7 +366,7 @@ main (int argc, char *argv[])
 
     for (n = 0; (c = iobuf_get (iobuf)) != -1; n ++)
       {
-	// printf ("%d: `%c'\n", n, c);
+	/* printf ("%d: `%c'\n", n, c);  */
 	buffer[n] = c;
       }
 
diff --git a/doc/HACKING b/doc/HACKING
index c1cd3480d..5d720172f 100644
--- a/doc/HACKING
+++ b/doc/HACKING
@@ -32,11 +32,31 @@ TAB, will not exceed 80 columns.  If you want to add text which shall
 not be copied to the ChangeLog, separate it by a line consisting of
 two dashes at the begin of a line.
 
-Typo fixes and documentation updates don't need a ChangeLog Entry,
+The one-line summary usually starts with a keyword to identify the
+mainly affected subsystem.  If more than one keyword is required the
+are delimited by a comma (e.g. =scd,w32:=). Commonly found keywords
+are
+
+ - agent   :: The gpg-agent component
+ - ssh     :: The ssh-agent part of the agent
+ - common  :: Code in common
+ - iobuf   :: The IOBUF system in common
+ - gpg     :: The gpg or gpgv components
+ - gpgsm   :: The gpgsm component
+ - scd     :: The scdaemon component
+ - ccid    :: The CCID driver in scdaemon
+ - dirmngr :: The dirmngr component
+ - w32     :: Windows related code
+ - po      :: Translations
+ - build   :: Changes to the build system
+ - speedo  :: Speedo build system specific changes
+ - doc     :: Documentation changes
+
+Typo fixes and documentation updates don't need a ChangeLog entry;
 thus you would use a commit message like
 
 #+begin_example
-Fix type in a comment
+Fix typo in a comment
 
 --
 #+end_example
@@ -54,7 +74,6 @@ Note that such a comment will be removed if the git commit option
 =--cleanup=scissor= is used.
 
 
-
 ** License policy
 
   GnuPG is licensed under the GPLv3+ with some files under a mixed
@@ -104,6 +123,12 @@ Note that such a comment will be removed if the git commit option
   need.  If you really need to do it, use a separate commit for such a
   change.
 
+  - C99 syntax should not be used; stick to C90.
+  - Please do not use C++ =//= style comments.
+  - Try to fit lines into 80 columns.
+  - Ignore signed/unsigned pointer mismatches
+  - No arithmetic on void pointers; cast to char* first.
+
 ** Commit log keywords
 
   - GnuPG-bug-id :: Values are comma or space delimited bug numbers
@@ -156,7 +181,6 @@ Note that such a comment will be removed if the git commit option
    the git repositories.  In case of problems, don't hesitate to ask
    on the gnupg-devel mailing for help.
 
-
 * Debug hints
 
   See the manual for some hints.