diff --git a/src/util/scanner.c b/src/util/scanner.c
index f986d8e1f..c4ed04715 100644
--- a/src/util/scanner.c
+++ b/src/util/scanner.c
@@ -144,7 +144,7 @@ init_scanner_info(struct scanner_info *scanner_info)
 				scan_table[index] |= info[i].bits;
 
 		} else {
-			char *string = info[i].data.string.source;
+			const char *string = info[i].data.string.source;
 			int pos = info[i].data.string.length - 1;
 
 			assert(info[i].type == SCAN_STRING && pos >= 0);
diff --git a/src/util/scanner.h b/src/util/scanner.h
index 69cda1231..4662be292 100644
--- a/src/util/scanner.h
+++ b/src/util/scanner.h
@@ -42,8 +42,8 @@ struct scanner_token {
 
 enum scan_type { SCAN_RANGE, SCAN_STRING, SCAN_END };
 union scan_table_data {
-	struct { char *source; long length; } string;
-	struct { unsigned char *start; long end; } range;
+	struct { const char *source; long length; } string;
+	struct { const unsigned char *start; long end; } range;
 };
 
 struct scan_table_info {