3 files changed, 8 insertions, 6 deletions
diff --git a/Makefile b/Makefile
index 083a2dcc..4f29ec17 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 CC=gcc
-CFLAGS=-O -g -Wall
+CFLAGS=-O -g -Wall -Wwrite-strings
 LDFLAGS=-g
 AR=ar
 
diff --git a/pre-process.c b/pre-process.c
index 2481ffc1..e2045ff7 100644
--- a/pre-process.c
+++ b/pre-process.c
@@ -95,7 +95,7 @@ static void replace_with_integer(struct token *token, unsigned int val)
 
 static void replace_with_defined(struct token *token)
 {
-	static char *string[] = { "0", "1" };
+	static const char *string[] = { "0", "1" };
 	int defined = 0;
 	if (token_type(token) != TOKEN_IDENT)
 		warning(token->pos, "operator \"defined\" requires an identifier");
@@ -382,11 +382,13 @@ static int merge(struct token *left, struct token *right)
 		left->pos.noexpand = 0;
 		return 1;
 
-	case TOKEN_NUMBER:
+	case TOKEN_NUMBER: {
+		char *number = __alloc_bytes(strlen(buffer) + 1);
+		memcpy(number, buffer, strlen(buffer) + 1);
 		token_type(left) = TOKEN_NUMBER;	/* could be . + num */
-		left->number = __alloc_bytes(strlen(buffer) + 1);
-		memcpy(left->number, buffer, strlen(buffer) + 1);
+		left->number = number;
 		return 1;
+	}
 
 	case TOKEN_SPECIAL:
 		if (buffer[2] && buffer[3])
diff --git a/token.h b/token.h
index ecb8ea01..d4defd7e 100644
--- a/token.h
+++ b/token.h
@@ -150,7 +150,7 @@ struct token {
 	struct position pos;
 	struct token *next;
 	union {
-		char *number;
+		const char *number;
 		struct ident *ident;
 		unsigned int special;
 		struct string *string;