diff --git a/library/use_psa_helpers.h b/library/use_psa_helpers.h
index 6b63ce8..e9a1335 100644
--- a/library/use_psa_helpers.h
+++ b/library/use_psa_helpers.h
@@ -1,8 +1,10 @@
 /**
  *  Internal macros for parts of the code governed by MBEDTLS_USE_PSA_CRYPTO.
- *  These macros allow checking if an algorithm is available, either via the
- *  legacy API or the PSA Crypto API, depending on MBEDTLS_USE_PSA_CRYPTO.
- *  When possible, they're named after the corresponding PSA_WANT_ macro.
+ *  Some macros allow checking if an algorithm is available, either via the
+ *  legacy API or the PSA Crypto API, depending on MBEDTLS_USE_PSA_CRYPTO;
+ *  when possible, they're named after the corresponding PSA_WANT_ macro.
+ *  Other macros provide max sizes or similar information in a USE_PSA-aware
+ *  way; they're name after a similar constant from the legacy API or PSA.
  *
  *  Copyright The Mbed TLS Contributors
  *  SPDX-License-Identifier: Apache-2.0
@@ -55,4 +57,11 @@
 #define MBEDTLS_USE_PSA_WANT_ALG_SHA_512
 #endif
 
+/* Hash information */
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+#define MBEDTLS_USE_PSA_MD_MAX_SIZE PSA_HASH_MAX_SIZE
+#else
+#define MBEDTLS_USE_PSA_MD_MAX_SIZE MBEDTLS_MD_MAX_SIZE
+#endif
+
 #endif /* MBEDTLS_USE_PSA_HELPERS_H */