diff --git a/library/aes.c b/library/aes.c
index ced8a32..b1a5c3e 100644
--- a/library/aes.c
+++ b/library/aes.c
@@ -53,6 +53,7 @@
 #endif
 
 #include "mbedtls/platform.h"
+#include "ctr.h"
 
 /*
  * This is a convenience shorthand macro to check if we need reverse S-box and
@@ -1456,11 +1457,7 @@
             if (ret != 0) {
                 goto exit;
             }
-            for (int j = 16; j > 0; j--) {
-                if (++nonce_counter[j - 1] != 0) {
-                    break;
-                }
-            }
+            mbedtls_ctr_increment_counter(nonce_counter);
         } else {
             n -= offset;
         }
diff --git a/library/ctr_drbg.c b/library/ctr_drbg.c
index da34f95..f3995f7 100644
--- a/library/ctr_drbg.c
+++ b/library/ctr_drbg.c
@@ -14,6 +14,7 @@
 
 #if defined(MBEDTLS_CTR_DRBG_C)
 
+#include "ctr.h"
 #include "mbedtls/ctr_drbg.h"
 #include "mbedtls/platform_util.h"
 #include "mbedtls/error.h"
@@ -333,7 +334,7 @@
 {
     unsigned char tmp[MBEDTLS_CTR_DRBG_SEEDLEN];
     unsigned char *p = tmp;
-    int i, j;
+    int j;
     int ret = 0;
 #if !defined(MBEDTLS_AES_C)
     psa_status_t status;
@@ -346,11 +347,7 @@
         /*
          * Increase counter
          */
-        for (i = MBEDTLS_CTR_DRBG_BLOCKSIZE; i > 0; i--) {
-            if (++ctx->counter[i - 1] != 0) {
-                break;
-            }
-        }
+        mbedtls_ctr_increment_counter(ctx->counter);
 
         /*
          * Crypt counter block
@@ -652,13 +649,9 @@
 
     while (output_len > 0) {
         /*
-         * Increase counter
+         * Increase counter (treat it as a 128-bit big-endian integer).
          */
-        for (i = MBEDTLS_CTR_DRBG_BLOCKSIZE; i > 0; i--) {
-            if (++ctx->counter[i - 1] != 0) {
-                break;
-            }
-        }
+        mbedtls_ctr_increment_counter(ctx->counter);
 
         /*
          * Crypt counter block