diff --git a/commit.h b/commit.h
index 4d452dc96d..011ddb146f 100644
--- a/commit.h
+++ b/commit.h
@@ -79,6 +79,9 @@ enum cmit_fmt {
 };
 
 struct pretty_print_context {
+	/*
+	 * Callers should tweak these to change the behavior of pp_* functions.
+	 */
 	enum cmit_fmt fmt;
 	int abbrev;
 	const char *subject;
@@ -92,6 +95,11 @@ struct pretty_print_context {
 	const char *output_encoding;
 	struct string_list *mailmap;
 	int color;
+
+	/*
+	 * Fields below here are manipulated internally by pp_* functions and
+	 * should not be counted on by callers.
+	 */
 };
 
 struct userformat_want {
@@ -111,20 +119,20 @@ extern void userformat_find_requirements(const char *fmt, struct userformat_want
 extern void format_commit_message(const struct commit *commit,
 				  const char *format, struct strbuf *sb,
 				  const struct pretty_print_context *context);
-extern void pretty_print_commit(const struct pretty_print_context *pp,
+extern void pretty_print_commit(struct pretty_print_context *pp,
 				const struct commit *commit,
 				struct strbuf *sb);
 extern void pp_commit_easy(enum cmit_fmt fmt, const struct commit *commit,
 			   struct strbuf *sb);
-void pp_user_info(const struct pretty_print_context *pp,
+void pp_user_info(struct pretty_print_context *pp,
 		  const char *what, struct strbuf *sb,
 		  const char *line, const char *encoding);
-void pp_title_line(const struct pretty_print_context *pp,
+void pp_title_line(struct pretty_print_context *pp,
 		   const char **msg_p,
 		   struct strbuf *sb,
 		   const char *encoding,
 		   int need_8bit_cte);
-void pp_remainder(const struct pretty_print_context *pp,
+void pp_remainder(struct pretty_print_context *pp,
 		  const char **msg_p,
 		  struct strbuf *sb,
 		  int indent);
diff --git a/pretty.c b/pretty.c
index 9e431545d8..68cd7a035b 100644
--- a/pretty.c
+++ b/pretty.c
@@ -406,7 +406,7 @@ static const char *show_ident_date(const struct ident_split *ident,
 	return show_date(date, tz, mode);
 }
 
-void pp_user_info(const struct pretty_print_context *pp,
+void pp_user_info(struct pretty_print_context *pp,
 		  const char *what, struct strbuf *sb,
 		  const char *line, const char *encoding)
 {
@@ -1514,7 +1514,7 @@ void format_commit_message(const struct commit *commit,
 	free(context.signature_check.signer);
 }
 
-static void pp_header(const struct pretty_print_context *pp,
+static void pp_header(struct pretty_print_context *pp,
 		      const char *encoding,
 		      const struct commit *commit,
 		      const char **msg_p,
@@ -1575,7 +1575,7 @@ static void pp_header(const struct pretty_print_context *pp,
 	}
 }
 
-void pp_title_line(const struct pretty_print_context *pp,
+void pp_title_line(struct pretty_print_context *pp,
 		   const char **msg_p,
 		   struct strbuf *sb,
 		   const char *encoding,
@@ -1618,7 +1618,7 @@ void pp_title_line(const struct pretty_print_context *pp,
 	strbuf_release(&title);
 }
 
-void pp_remainder(const struct pretty_print_context *pp,
+void pp_remainder(struct pretty_print_context *pp,
 		  const char **msg_p,
 		  struct strbuf *sb,
 		  int indent)
@@ -1650,7 +1650,7 @@ void pp_remainder(const struct pretty_print_context *pp,
 	}
 }
 
-void pretty_print_commit(const struct pretty_print_context *pp,
+void pretty_print_commit(struct pretty_print_context *pp,
 			 const struct commit *commit,
 			 struct strbuf *sb)
 {