diff --git a/include/game.h b/include/game.h
index ca18eae..7451153 100644
--- a/include/game.h
+++ b/include/game.h
@@ -6,7 +6,13 @@
 #define MAX_FILENAME 256
 #define MAX_MESSAGE 256
 
-#define MAX_WORDS 10000
+/* Reduce MAX_WORDS for DOS to avoid stack overflow */
+#ifdef PLATFORM_DOS
+    #define MAX_WORDS 2000
+#else
+    #define MAX_WORDS 10000
+#endif
+
 #define WORD_LENGTH 5
 #define MAX_GUESSES 6
 
diff --git a/src/game.c b/src/game.c
index 3afe2a7..a27c519 100644
--- a/src/game.c
+++ b/src/game.c
@@ -36,9 +36,10 @@ void init_game(GameState *game) {
 
 /* Check guess against target word */
 void check_guess(GameState *game, const char *guess, int *colors) {
+    int i, j;
+
     char target_copy[WORD_LENGTH + 1];
     char guess_copy[WORD_LENGTH + 1];
-    int i, j;
     int target_used[WORD_LENGTH] = {0};
 
     strcpy(target_copy, game->target_word);
@@ -46,7 +47,7 @@ void check_guess(GameState *game, const char *guess, int *colors) {
 
     /* Ensure uppercase */
     for (i = 0; i < WORD_LENGTH; i++) {
-        guess_copy[i] = toupper(guess_copy[i]);
+        guess_copy[i] = toupper((unsigned char)guess_copy[i]);
     }
 
     /* Initialize all as absent */
@@ -97,7 +98,7 @@ int make_guess(GameState *game, const char *guess) {
 
     strcpy(upper_guess, guess);
     for (i = 0; i < WORD_LENGTH; i++) {
-        upper_guess[i] = toupper(upper_guess[i]);
+        upper_guess[i] = toupper((unsigned char)upper_guess[i]);
     }
 
     if (!is_valid_word(game, upper_guess)) {
diff --git a/src/main.c b/src/main.c
index 89f3ea6..0e0529c 100644
--- a/src/main.c
+++ b/src/main.c
@@ -196,7 +196,7 @@ int main_game_loop(int argc, char *argv[]) {
             }
         } else if ((key >= 'a' && key <= 'z') || (key >= 'A' && key <= 'Z')) {
             if (game.current_guess_length < WORD_LENGTH) {
-                game.current_guess[game.current_guess_length] = toupper(key);
+                game.current_guess[game.current_guess_length] = toupper((unsigned char)key);
                 game.current_guess_length++;
                 game.current_guess[game.current_guess_length] = '\0';
                 strcpy(message, "");
diff --git a/src/ui.c b/src/ui.c
index f7d69f3..34e9109 100644
--- a/src/ui.c
+++ b/src/ui.c
@@ -143,7 +143,7 @@ void draw_message(WINDOW *win, const char *message, const int y, const int color
 
 /* Draw game instructions */
 void draw_instructions(WINDOW *win, int y) {
-    const char *instructions[] = {
+    static const char *instructions[] = {
         "Guess the 5-letter word in 6 tries!",
         "",
         "Colors: GREEN=Correct, YELLOW=Wrong position, RED=Not in word",
diff --git a/src/words.c b/src/words.c
index bf1d67d..e9284e5 100644
--- a/src/words.c
+++ b/src/words.c
@@ -11,7 +11,7 @@
 #include <ctype.h>
 
 /* Try to open a wordlist file, using multiple fallback locations */
-static FILE* open_wordlist(const char *filename) {
+static FILE *open_wordlist(const char *filename) {
     FILE *file;
     char filepath[512];
 #if HAS_HOME_ENV
@@ -47,7 +47,7 @@ static FILE* open_wordlist(const char *filename) {
 void to_upper(char *str) {
     int i;
     for (i = 0; str[i]; i++) {
-        str[i] = toupper(str[i]);
+        str[i] = toupper((unsigned char)str[i]);
     }
 }