diff --git a/library/psa_crypto_cipher.c b/library/psa_crypto_cipher.c
index 6d0378b..022bdfa 100644
--- a/library/psa_crypto_cipher.c
+++ b/library/psa_crypto_cipher.c
@@ -552,9 +552,21 @@
     uint8_t *output, size_t output_size, size_t *output_length)
 {
     psa_status_t status = PSA_ERROR_GENERIC_ERROR;
-    uint8_t temp_output_buffer[MBEDTLS_MAX_BLOCK_LENGTH];
     size_t invalid_padding = 0;
 
+    uint8_t temp_output_buffer[MBEDTLS_MAX_BLOCK_LENGTH] = { 0 };
+    if (output_size > sizeof(temp_output_buffer)) {
+        output_size = sizeof(temp_output_buffer);
+    }
+    /* We will copy output_size bytes from temp_output_buffer to the
+     * output buffer. We can't use *output_length to determine how
+     * much to copy because we must not leak that value through timing
+     * when doing decryption with unpadding. But the underlying function
+     * is not guaranteed to write beyond *output_length. To ensure we don't
+     * leak the former content of the stack to the caller, wipe that
+     * former content. */
+    memset(temp_output_buffer, 0, output_size);
+
     if (operation->ctx.cipher.unprocessed_len != 0) {
         if (operation->alg == PSA_ALG_ECB_NO_PADDING ||
             operation->alg == PSA_ALG_CBC_NO_PADDING) {
@@ -572,22 +584,26 @@
         goto exit;
     }
 
-    if (*output_length == 0) {
+    if (output_size == 0) {
         ; /* Nothing to copy. Note that output may be NULL in this case. */
-    } else if (output_size >= *output_length) {
-        memcpy(output, temp_output_buffer, *output_length);
     } else {
-        status = PSA_ERROR_BUFFER_TOO_SMALL;
+        /* Do not use the value of *output_length to determine how much
+         * to copy. When decrypting a padded cipher, the output length is
+         * sensitive, and leaking it could allow a padding oracle attack. */
+        memcpy(output, temp_output_buffer, output_size);
     }
 
+    status = mbedtls_ct_error_if_else_0(invalid_padding,
+                                        PSA_ERROR_INVALID_PADDING);
+    mbedtls_ct_condition_t buffer_too_small =
+        mbedtls_ct_uint_lt(output_size, *output_length);
+    status = mbedtls_ct_error_if(buffer_too_small,
+                                 PSA_ERROR_BUFFER_TOO_SMALL,
+                                 status);
+
 exit:
     mbedtls_platform_zeroize(temp_output_buffer,
                              sizeof(temp_output_buffer));
-
-    if (status == PSA_SUCCESS) {
-        status = mbedtls_ct_size_if_else_0(invalid_padding,
-                                           PSA_ERROR_INVALID_PADDING);
-    }
     return status;
 }