diff --git a/library/ccm.c b/library/ccm.c
index 2d2695e979..79a04a275a 100644
--- a/library/ccm.c
+++ b/library/ccm.c
@@ -33,6 +33,7 @@
 #include "mbedtls/ccm.h"
 #include "mbedtls/platform_util.h"
 #include "mbedtls/error.h"
+#include "mbedtls/constant_time.h"
 
 #include <string.h>
 
@@ -362,7 +363,6 @@ int mbedtls_ccm_star_auth_decrypt(mbedtls_ccm_context *ctx, size_t length,
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     unsigned char check_tag[16];
-    unsigned char i;
     int diff;
 
     CCM_VALIDATE_RET(ctx != NULL);
@@ -379,9 +379,7 @@ int mbedtls_ccm_star_auth_decrypt(mbedtls_ccm_context *ctx, size_t length,
     }
 
     /* Check tag in "constant-time" */
-    for (diff = 0, i = 0; i < tag_len; i++) {
-        diff |= tag[i] ^ check_tag[i];
-    }
+    diff = mbedtls_ct_memcmp(tag, check_tag, tag_len);
 
     if (diff != 0) {
         mbedtls_platform_zeroize(output, length);
diff --git a/library/chachapoly.c b/library/chachapoly.c
index ceb429287b..547ffb2ed2 100644
--- a/library/chachapoly.c
+++ b/library/chachapoly.c
@@ -25,6 +25,7 @@
 #include "mbedtls/chachapoly.h"
 #include "mbedtls/platform_util.h"
 #include "mbedtls/error.h"
+#include "mbedtls/constant_time.h"
 
 #include <string.h>
 
@@ -337,7 +338,6 @@ int mbedtls_chachapoly_auth_decrypt(mbedtls_chachapoly_context *ctx,
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     unsigned char check_tag[16];
-    size_t i;
     int diff;
     CHACHAPOLY_VALIDATE_RET(ctx   != NULL);
     CHACHAPOLY_VALIDATE_RET(nonce != NULL);
@@ -353,9 +353,7 @@ int mbedtls_chachapoly_auth_decrypt(mbedtls_chachapoly_context *ctx,
     }
 
     /* Check tag in "constant-time" */
-    for (diff = 0, i = 0; i < sizeof(check_tag); i++) {
-        diff |= tag[i] ^ check_tag[i];
-    }
+    diff = mbedtls_ct_memcmp(tag, check_tag, sizeof(check_tag));
 
     if (diff != 0) {
         mbedtls_platform_zeroize(output, length);
diff --git a/library/gcm.c b/library/gcm.c
index 0c958c729a..71e7b2e9bc 100644
--- a/library/gcm.c
+++ b/library/gcm.c
@@ -35,6 +35,7 @@
 #include "mbedtls/platform.h"
 #include "mbedtls/platform_util.h"
 #include "mbedtls/error.h"
+#include "mbedtls/constant_time.h"
 
 #include <string.h>
 
@@ -478,7 +479,6 @@ int mbedtls_gcm_auth_decrypt(mbedtls_gcm_context *ctx,
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     unsigned char check_tag[16];
-    size_t i;
     int diff;
 
     GCM_VALIDATE_RET(ctx != NULL);
@@ -495,9 +495,7 @@ int mbedtls_gcm_auth_decrypt(mbedtls_gcm_context *ctx,
     }
 
     /* Check tag in "constant-time" */
-    for (diff = 0, i = 0; i < tag_len; i++) {
-        diff |= tag[i] ^ check_tag[i];
-    }
+    diff = mbedtls_ct_memcmp(tag, check_tag, tag_len);
 
     if (diff != 0) {
         mbedtls_platform_zeroize(output, length);