diff --git a/grep.c b/grep.c
index 79598f245f..14fe8a0fd2 100644
--- a/grep.c
+++ b/grep.c
@@ -867,7 +867,7 @@ void free_grep_patterns(struct grep_opt *opt)
 	free_pattern_expr(opt->pattern_expression);
 }
 
-static char *end_of_line(char *cp, unsigned long *left)
+static const char *end_of_line(const char *cp, unsigned long *left)
 {
 	unsigned long l = *left;
 	while (l && *cp != '\n') {
@@ -908,7 +908,8 @@ static void show_name(struct grep_opt *opt, const char *name)
 	opt->output(opt, opt->null_following_name ? "\0" : "\n", 1);
 }
 
-static int patmatch(struct grep_pat *p, char *line, char *eol,
+static int patmatch(struct grep_pat *p,
+		    const char *line, const char *eol,
 		    regmatch_t *match, int eflags)
 {
 	int hit;
@@ -922,20 +923,16 @@ static int patmatch(struct grep_pat *p, char *line, char *eol,
 	return hit;
 }
 
-static int strip_timestamp(char *bol, char **eol_p)
+static void strip_timestamp(const char *bol, const char **eol_p)
 {
-	char *eol = *eol_p;
-	int ch;
+	const char *eol = *eol_p;
 
 	while (bol < --eol) {
 		if (*eol != '>')
 			continue;
 		*eol_p = ++eol;
-		ch = *eol;
-		*eol = '\0';
-		return ch;
+		break;
 	}
-	return 0;
 }
 
 static struct {
@@ -947,12 +944,12 @@ static struct {
 	{ "reflog ", 7 },
 };
 
-static int match_one_pattern(struct grep_pat *p, char *bol, char *eol,
+static int match_one_pattern(struct grep_pat *p,
+			     const char *bol, const char *eol,
 			     enum grep_context ctx,
 			     regmatch_t *pmatch, int eflags)
 {
 	int hit = 0;
-	int saved_ch = 0;
 	const char *start = bol;
 
 	if ((p->token != GREP_PATTERN) &&
@@ -971,7 +968,7 @@ static int match_one_pattern(struct grep_pat *p, char *bol, char *eol,
 		switch (p->field) {
 		case GREP_HEADER_AUTHOR:
 		case GREP_HEADER_COMMITTER:
-			saved_ch = strip_timestamp(bol, &eol);
+			strip_timestamp(bol, &eol);
 			break;
 		default:
 			break;
@@ -1021,8 +1018,6 @@ static int match_one_pattern(struct grep_pat *p, char *bol, char *eol,
 				goto again;
 		}
 	}
-	if (p->token == GREP_PATTERN_HEAD && saved_ch)
-		*eol = saved_ch;
 	if (hit) {
 		pmatch[0].rm_so += bol - start;
 		pmatch[0].rm_eo += bol - start;
@@ -1030,8 +1025,9 @@ static int match_one_pattern(struct grep_pat *p, char *bol, char *eol,
 	return hit;
 }
 
-static int match_expr_eval(struct grep_opt *opt, struct grep_expr *x, char *bol,
-			   char *eol, enum grep_context ctx, ssize_t *col,
+static int match_expr_eval(struct grep_opt *opt, struct grep_expr *x,
+			   const char *bol, const char *eol,
+			   enum grep_context ctx, ssize_t *col,
 			   ssize_t *icol, int collect_hits)
 {
 	int h = 0;
@@ -1098,7 +1094,8 @@ static int match_expr_eval(struct grep_opt *opt, struct grep_expr *x, char *bol,
 	return h;
 }
 
-static int match_expr(struct grep_opt *opt, char *bol, char *eol,
+static int match_expr(struct grep_opt *opt,
+		      const char *bol, const char *eol,
 		      enum grep_context ctx, ssize_t *col,
 		      ssize_t *icol, int collect_hits)
 {
@@ -1106,7 +1103,8 @@ static int match_expr(struct grep_opt *opt, char *bol, char *eol,
 	return match_expr_eval(opt, x, bol, eol, ctx, col, icol, collect_hits);
 }
 
-static int match_line(struct grep_opt *opt, char *bol, char *eol,
+static int match_line(struct grep_opt *opt,
+		      const char *bol, const char *eol,
 		      ssize_t *col, ssize_t *icol,
 		      enum grep_context ctx, int collect_hits)
 {
@@ -1138,7 +1136,8 @@ static int match_line(struct grep_opt *opt, char *bol, char *eol,
 	return hit;
 }
 
-static int match_next_pattern(struct grep_pat *p, char *bol, char *eol,
+static int match_next_pattern(struct grep_pat *p,
+			      const char *bol, const char *eol,
 			      enum grep_context ctx,
 			      regmatch_t *pmatch, int eflags)
 {
@@ -1159,7 +1158,8 @@ static int match_next_pattern(struct grep_pat *p, char *bol, char *eol,
 	return 1;
 }
 
-static int next_match(struct grep_opt *opt, char *bol, char *eol,
+static int next_match(struct grep_opt *opt,
+		      const char *bol, const char *eol,
 		      enum grep_context ctx, regmatch_t *pmatch, int eflags)
 {
 	struct grep_pat *p;
@@ -1215,7 +1215,8 @@ static void show_line_header(struct grep_opt *opt, const char *name,
 	}
 }
 
-static void show_line(struct grep_opt *opt, char *bol, char *eol,
+static void show_line(struct grep_opt *opt,
+		      const char *bol, const char *eol,
 		      const char *name, unsigned lno, ssize_t cno, char sign)
 {
 	int rest = eol - bol;
@@ -1246,7 +1247,6 @@ static void show_line(struct grep_opt *opt, char *bol, char *eol,
 	if (opt->color || opt->only_matching) {
 		regmatch_t match;
 		enum grep_context ctx = GREP_CONTEXT_BODY;
-		int ch = *eol;
 		int eflags = 0;
 
 		if (opt->color) {
@@ -1261,7 +1261,6 @@ static void show_line(struct grep_opt *opt, char *bol, char *eol,
 			else if (sign == '=')
 				line_color = opt->colors[GREP_COLOR_FUNCTION];
 		}
-		*eol = '\0';
 		while (next_match(opt, bol, eol, ctx, &match, eflags)) {
 			if (match.rm_so == match.rm_eo)
 				break;
@@ -1279,7 +1278,6 @@ static void show_line(struct grep_opt *opt, char *bol, char *eol,
 			rest -= match.rm_eo;
 			eflags = REG_NOTBOL;
 		}
-		*eol = ch;
 	}
 	if (!opt->only_matching) {
 		output_color(opt, bol, rest, line_color);
@@ -1307,7 +1305,8 @@ static inline void grep_attr_unlock(void)
 		pthread_mutex_unlock(&grep_attr_mutex);
 }
 
-static int match_funcname(struct grep_opt *opt, struct grep_source *gs, char *bol, char *eol)
+static int match_funcname(struct grep_opt *opt, struct grep_source *gs,
+			  const char *bol, const char *eol)
 {
 	xdemitconf_t *xecfg = opt->priv;
 	if (xecfg && !xecfg->find_func) {
@@ -1334,10 +1333,10 @@ static int match_funcname(struct grep_opt *opt, struct grep_source *gs, char *bo
 }
 
 static void show_funcname_line(struct grep_opt *opt, struct grep_source *gs,
-			       char *bol, unsigned lno)
+			       const char *bol, unsigned lno)
 {
 	while (bol > gs->buf) {
-		char *eol = --bol;
+		const char *eol = --bol;
 
 		while (bol > gs->buf && bol[-1] != '\n')
 			bol--;
@@ -1356,7 +1355,7 @@ static void show_funcname_line(struct grep_opt *opt, struct grep_source *gs,
 static int is_empty_line(const char *bol, const char *eol);
 
 static void show_pre_context(struct grep_opt *opt, struct grep_source *gs,
-			     char *bol, char *end, unsigned lno)
+			     const char *bol, const char *end, unsigned lno)
 {
 	unsigned cur = lno, from = 1, funcname_lno = 0, orig_from;
 	int funcname_needed = !!opt->funcname, comment_needed = 0;
@@ -1376,8 +1375,8 @@ static void show_pre_context(struct grep_opt *opt, struct grep_source *gs,
 
 	/* Rewind. */
 	while (bol > gs->buf && cur > from) {
-		char *next_bol = bol;
-		char *eol = --bol;
+		const char *next_bol = bol;
+		const char *eol = --bol;
 
 		while (bol > gs->buf && bol[-1] != '\n')
 			bol--;
@@ -1408,7 +1407,7 @@ static void show_pre_context(struct grep_opt *opt, struct grep_source *gs,
 
 	/* Back forward. */
 	while (cur < lno) {
-		char *eol = bol, sign = (cur == funcname_lno) ? '=' : '-';
+		const char *eol = bol, sign = (cur == funcname_lno) ? '=' : '-';
 
 		while (*eol != '\n')
 			eol++;
@@ -1436,12 +1435,12 @@ static int should_lookahead(struct grep_opt *opt)
 static int look_ahead(struct grep_opt *opt,
 		      unsigned long *left_p,
 		      unsigned *lno_p,
-		      char **bol_p)
+		      const char **bol_p)
 {
 	unsigned lno = *lno_p;
-	char *bol = *bol_p;
+	const char *bol = *bol_p;
 	struct grep_pat *p;
-	char *sp, *last_bol;
+	const char *sp, *last_bol;
 	regoff_t earliest = -1;
 
 	for (p = opt->pattern_list; p; p = p->next) {
@@ -1543,8 +1542,8 @@ static int is_empty_line(const char *bol, const char *eol)
 
 static int grep_source_1(struct grep_opt *opt, struct grep_source *gs, int collect_hits)
 {
-	char *bol;
-	char *peek_bol = NULL;
+	const char *bol;
+	const char *peek_bol = NULL;
 	unsigned long left;
 	unsigned lno = 1;
 	unsigned last_hit = 0;
@@ -1626,7 +1625,7 @@ static int grep_source_1(struct grep_opt *opt, struct grep_source *gs, int colle
 	bol = gs->buf;
 	left = gs->size;
 	while (left) {
-		char *eol, ch;
+		const char *eol;
 		int hit;
 		ssize_t cno;
 		ssize_t col = -1, icol = -1;
@@ -1647,14 +1646,11 @@ static int grep_source_1(struct grep_opt *opt, struct grep_source *gs, int colle
 		    && look_ahead(opt, &left, &lno, &bol))
 			break;
 		eol = end_of_line(bol, &left);
-		ch = *eol;
-		*eol = 0;
 
 		if ((ctx == GREP_CONTEXT_HEAD) && (eol == bol))
 			ctx = GREP_CONTEXT_BODY;
 
 		hit = match_line(opt, bol, eol, &col, &icol, ctx, collect_hits);
-		*eol = ch;
 
 		if (collect_hits)
 			goto next_line;
@@ -1713,7 +1709,7 @@ static int grep_source_1(struct grep_opt *opt, struct grep_source *gs, int colle
 		}
 		if (show_function && (!peek_bol || peek_bol < bol)) {
 			unsigned long peek_left = left;
-			char *peek_eol = eol;
+			const char *peek_eol = eol;
 
 			/*
 			 * Trailing empty lines are not interesting.
@@ -1825,7 +1821,8 @@ int grep_source(struct grep_opt *opt, struct grep_source *gs)
 	return grep_source_1(opt, gs, 0);
 }
 
-static void grep_source_init_buf(struct grep_source *gs, char *buf,
+static void grep_source_init_buf(struct grep_source *gs,
+				 const char *buf,
 				 unsigned long size)
 {
 	gs->type = GREP_SOURCE_BUF;
@@ -1837,7 +1834,7 @@ static void grep_source_init_buf(struct grep_source *gs, char *buf,
 	gs->identifier = NULL;
 }
 
-int grep_buffer(struct grep_opt *opt, char *buf, unsigned long size)
+int grep_buffer(struct grep_opt *opt, const char *buf, unsigned long size)
 {
 	struct grep_source gs;
 	int r;
@@ -1889,7 +1886,9 @@ void grep_source_clear_data(struct grep_source *gs)
 	switch (gs->type) {
 	case GREP_SOURCE_FILE:
 	case GREP_SOURCE_OID:
-		FREE_AND_NULL(gs->buf);
+		/* these types own the buffer */
+		free((char *)gs->buf);
+		gs->buf = NULL;
 		gs->size = 0;
 		break;
 	case GREP_SOURCE_BUF:
diff --git a/grep.h b/grep.h
index 128007db65..3cb8a83ae8 100644
--- a/grep.h
+++ b/grep.h
@@ -189,7 +189,7 @@ void append_grep_pattern(struct grep_opt *opt, const char *pat, const char *orig
 void append_header_grep_pattern(struct grep_opt *, enum grep_header_field, const char *);
 void compile_grep_patterns(struct grep_opt *opt);
 void free_grep_patterns(struct grep_opt *opt);
-int grep_buffer(struct grep_opt *opt, char *buf, unsigned long size);
+int grep_buffer(struct grep_opt *opt, const char *buf, unsigned long size);
 
 struct grep_source {
 	char *name;
@@ -202,7 +202,7 @@ struct grep_source {
 	void *identifier;
 	struct repository *repo; /* if GREP_SOURCE_OID */
 
-	char *buf;
+	const char *buf;
 	unsigned long size;
 
 	char *path; /* for attribute lookups */