diff --git a/src/cac-aca.c b/src/cac-aca.c
index 9e305a8..e66b089 100644
--- a/src/cac-aca.c
+++ b/src/cac-aca.c
@@ -60,7 +60,7 @@ struct acr_entry {
     struct acr_access_method access_methods[MAX_ACCESS_METHODS];
 };
 struct acr_table {
-    unsigned int num_entries;
+    unsigned char num_entries;
     struct acr_entry entries[];
 };
 
diff --git a/tests/libcacard.c b/tests/libcacard.c
index 0c6cca1..18ccf6f 100644
--- a/tests/libcacard.c
+++ b/tests/libcacard.c
@@ -179,7 +179,7 @@ static void parse_acr(uint8_t *buf, int buflen)
 {
     uint8_t *p, *p_end;
     int have_applet_information = 0;
-    int num_entries = 0, num_entries_expected = -1;
+    uint8_t num_entries = 0, num_entries_expected = 255;
 
     p = buf;
     p_end = p + buflen - 2;
@@ -204,7 +204,7 @@ static void parse_acr(uint8_t *buf, int buflen)
         case 0x81: /* Num Applet/Objects */
         case 0x91: /* Num AMP Entries */
         case 0x94: /* Num Service Applet Entries */
-            g_assert_cmpint(num_entries_expected, ==, -1);
+            g_assert_cmpint(num_entries_expected, ==, 255);
             g_assert_cmpint(num_entries, ==, 0);
             num_entries_expected = *p;
             break;
@@ -230,7 +230,7 @@ static void parse_acr(uint8_t *buf, int buflen)
     /* Every response needs to have exactly one applet information tag */
     g_assert_cmpint(have_applet_information, ==, 1);
     /* The number of entries in the second tag matches the number of entries later */
-    if (num_entries_expected != -1) {
+    if (num_entries_expected != 255) {
         g_assert_cmpint(num_entries, ==, num_entries_expected);
     }
     /* nothing left to read */