diff --git a/src/document/css/parser.c b/src/document/css/parser.c
index a133149db..ee2bfe721 100644
--- a/src/document/css/parser.c
+++ b/src/document/css/parser.c
@@ -629,7 +629,7 @@ css_parse_ruleset(struct css_stylesheet *css, struct scanner *scanner)
 
 void
 css_parse_stylesheet(struct css_stylesheet *css, struct uri *base_uri,
-		     unsigned char *string, unsigned char *end)
+		     const unsigned char *string, const unsigned char *end)
 {
 	struct scanner scanner;
 
diff --git a/src/document/css/parser.h b/src/document/css/parser.h
index 645d0525e..67d00e215 100644
--- a/src/document/css/parser.h
+++ b/src/document/css/parser.h
@@ -23,6 +23,6 @@ void css_parse_properties(LIST_OF(struct css_property) *props,
  * given stylesheet @a css. If the selector is already in the stylesheet it
  * properties are added to the that selector. */
 void css_parse_stylesheet(struct css_stylesheet *css, struct uri *base_uri,
-			  unsigned char *string, unsigned char *end);
+			  const unsigned char *string, const unsigned char *end);
 
 #endif
diff --git a/src/document/css/scanner.c b/src/document/css/scanner.c
index 361b1a411..767c66431 100644
--- a/src/document/css/scanner.c
+++ b/src/document/css/scanner.c
@@ -124,7 +124,7 @@ struct scanner_info css_scanner_info = {
 static inline void
 scan_css_token(struct scanner *scanner, struct scanner_token *token)
 {
-	unsigned char *string = scanner->position;
+	const unsigned char *string = scanner->position;
 	unsigned char first_char = *string;
 	enum css_token_type type = CSS_TOKEN_GARBAGE;
 	int real_length = -1;
@@ -169,7 +169,7 @@ scan_css_token(struct scanner *scanner, struct scanner_token *token)
 		scan_css(scanner, string, CSS_CHAR_IDENT);
 
 		if (*string == '(') {
-			unsigned char *function_end = string + 1;
+			const unsigned char *function_end = string + 1;
 
 			/* Make sure that we have an ending ')' */
 			skip_css(scanner, function_end, ')');
@@ -193,8 +193,8 @@ scan_css_token(struct scanner *scanner, struct scanner_token *token)
 					 * we should of course handle escape
 					 * sequences .. but that will have to
 					 * be fixed later.  */
-					unsigned char *from = string + 1;
-					unsigned char *to = function_end - 1;
+					const unsigned char *from = string + 1;
+					const unsigned char *to = function_end - 1;
 
 					scan_css(scanner, from, CSS_CHAR_WHITESPACE);
 					scan_back_css(scanner, to, CSS_CHAR_WHITESPACE);
@@ -313,7 +313,7 @@ scan_css_token(struct scanner *scanner, struct scanner_token *token)
 			type = CSS_TOKEN_NONE;
 
 		} else {
-			unsigned char *sgml = string;
+			const unsigned char *sgml = string;
 
 			/* Skip anything looking like SGML "<!--" and "-->"
 			 * comments + <![CDATA[ and ]]> notations. */
diff --git a/src/document/dom/source.c b/src/document/dom/source.c
index 5faf1d35e..f195a8242 100644
--- a/src/document/dom/source.c
+++ b/src/document/dom/source.c
@@ -348,13 +348,13 @@ render_dom_document_start(struct dom_stack *stack, struct dom_node *node, void *
 				"attribute	{ color: magenta } "
 				"comment	{ color: aqua } "
 				"cdata-section	{ color: orange2 } ";
-			unsigned char *styles = (unsigned char *) default_colors;
 
 			i_want_struct_module_for_dom = 1;
 			/* When someone will get here earlier than at 4am,
 			 * this will be done in some init function, perhaps
 			 * not overriding the user's default stylesheet. */
-			css_parse_stylesheet(css, NULL, styles, styles + sizeof(default_colors));
+			css_parse_stylesheet(css, NULL, default_colors,
+					     default_colors + sizeof(default_colors));
 		}
 	}
 
diff --git a/src/protocol/bittorrent/bencoding.c b/src/protocol/bittorrent/bencoding.c
index 80dc5d67f..4765e9d5d 100644
--- a/src/protocol/bittorrent/bencoding.c
+++ b/src/protocol/bittorrent/bencoding.c
@@ -105,7 +105,7 @@ enum bencoding_token {
 static inline void
 scan_bencoding_token(struct scanner *scanner, struct scanner_token *token)
 {
-	unsigned char *string = scanner->position;
+	const unsigned char *string = scanner->position;
 	unsigned char first_char = *string;
 	enum bencoding_token type = BENCODING_TOKEN_NONE;
 	int real_length = -1;
@@ -136,7 +136,7 @@ scan_bencoding_token(struct scanner *scanner, struct scanner_token *token)
 		type = BENCODING_TOKEN_END;
 
 	} else if (is_bencoding_integer(first_char)) {
-		unsigned char *integer_start = string;
+		const unsigned char *integer_start = string;
 
 		/* Signedness. */
 		if (*string == '-') string++;
diff --git a/src/protocol/bittorrent/common.h b/src/protocol/bittorrent/common.h
index 3726844a1..263072f20 100644
--- a/src/protocol/bittorrent/common.h
+++ b/src/protocol/bittorrent/common.h
@@ -348,9 +348,7 @@ struct bittorrent_connection {
  * this structure.  So it is okay to make @c source point to data that
  * is part of a larger buffer.  Also, there is no @c magic member here.  */
 struct bittorrent_const_string {
-	/** @todo This is not yet actually const because that will
-	 * require changes in the scanner too.  */
-	unsigned char *source;
+	const unsigned char *source;
 	int length;
 };
 
diff --git a/src/protocol/bittorrent/piececache.c b/src/protocol/bittorrent/piececache.c
index 8db5bb375..16fa5499f 100644
--- a/src/protocol/bittorrent/piececache.c
+++ b/src/protocol/bittorrent/piececache.c
@@ -1080,7 +1080,7 @@ bittorrent_resume_writer(void *data, int fd)
 	uint32_t piece;
 
 	memcpy(&metafile.length, data, sizeof(metafile.length));
-	metafile.source = (unsigned char *) data + sizeof(metafile.length);
+	metafile.source = (const unsigned char *) data + sizeof(metafile.length);
 
 	if (parse_bittorrent_metafile(&meta, &metafile) != BITTORRENT_STATE_OK) {
 		done_bittorrent_meta(&meta);
diff --git a/src/util/scanner.c b/src/util/scanner.c
index 1545745f5..949d6016e 100644
--- a/src/util/scanner.c
+++ b/src/util/scanner.c
@@ -157,7 +157,7 @@ init_scanner_info(struct scanner_info *scanner_info)
 
 void
 init_scanner(struct scanner *scanner, struct scanner_info *scanner_info,
-	     unsigned char *string, unsigned char *end)
+	     const unsigned char *string, const unsigned char *end)
 {
 	if (!scanner_info->initialized) {
 		init_scanner_info(scanner_info);
diff --git a/src/util/scanner.h b/src/util/scanner.h
index a88462583..615142ebc 100644
--- a/src/util/scanner.h
+++ b/src/util/scanner.h
@@ -19,7 +19,7 @@ struct scanner_token {
 	int precedence;
 
 	/** The start of the token string and the token length */
-	unsigned char *string;
+	const unsigned char *string;
 	int length;
 };
 
@@ -87,7 +87,7 @@ struct scanner_info {
 /** Initializes the scanner.
  * @relates scanner */
 void init_scanner(struct scanner *scanner, struct scanner_info *scanner_info,
-		  unsigned char *string, unsigned char *end);
+		  const unsigned char *string, const unsigned char *end);
 
 /** The number of tokens in the scanners token table:
  * At best it should be big enough to contain properties with space separated
@@ -101,7 +101,7 @@ struct scanner {
 	/** The very start of the scanned string, the position in the string
 	 * where to scan next and the end of the string. If #position is NULL
 	 * it means that no more tokens can be retrieved from the string. */
-	unsigned char *string, *position, *end;
+	const unsigned char *string, *position, *end;
 
 	/** The current token and number of scanned tokens in the table.
 	 * If the number of scanned tokens is less than ::SCANNER_TOKENS