diff --git a/tests/psa-client-server/psasim/src/psa_ff_server.c b/tests/psa-client-server/psasim/src/psa_ff_server.c
index 7f97b9bf0f..b0737ec840 100644
--- a/tests/psa-client-server/psasim/src/psa_ff_server.c
+++ b/tests/psa-client-server/psasim/src/psa_ff_server.c
@@ -474,7 +474,7 @@ void psa_write(psa_handle_t msg_handle, uint32_t outvec_idx,
 
     while (sofar < num_bytes) {
         size_t sending = (num_bytes - sofar);
-        if (sending >= MAX_FRAGMENT_SIZE) {
+        if (sending > (MAX_FRAGMENT_SIZE - (sizeof(size_t) * 2))) {
             sending = MAX_FRAGMENT_SIZE - (sizeof(size_t) * 2);
         }
 
diff --git a/tests/psa-client-server/psasim/src/psa_sim_crypto_client.c b/tests/psa-client-server/psasim/src/psa_sim_crypto_client.c
index 28dff38d02..4200f6c04d 100644
--- a/tests/psa-client-server/psasim/src/psa_sim_crypto_client.c
+++ b/tests/psa-client-server/psasim/src/psa_sim_crypto_client.c
@@ -44,7 +44,7 @@ int psa_crypto_call(int function,
     invec.base = in_params;
     invec.len = in_params_len;
 
-    size_t max_receive = 8192;
+    size_t max_receive = 24576;
     uint8_t *receive = malloc(max_receive);
     if (receive == NULL) {
         fprintf(stderr, "FAILED to allocate %u bytes\n", (unsigned) max_receive);
@@ -119,6 +119,11 @@ fail:
 
 void mbedtls_psa_crypto_free(void)
 {
+    /* Do not try to close a connection that was never started.*/
+    if (handle == -1) {
+        return;
+    }
+
     CLIENT_PRINT("Closing handle");
     psa_close(handle);
     handle = -1;
diff --git a/tests/psa-client-server/psasim/src/psa_sim_generate.pl b/tests/psa-client-server/psasim/src/psa_sim_generate.pl
index ac238070c3..ac7b2419c7 100755
--- a/tests/psa-client-server/psasim/src/psa_sim_generate.pl
+++ b/tests/psa-client-server/psasim/src/psa_sim_generate.pl
@@ -349,7 +349,7 @@ int psa_crypto_call(int function,
     invec.base = in_params;
     invec.len = in_params_len;
 
-    size_t max_receive = 8192;
+    size_t max_receive = 24576;
     uint8_t *receive = malloc(max_receive);
     if (receive == NULL) {
         fprintf(stderr, "FAILED to allocate %u bytes\n", (unsigned) max_receive);
@@ -424,6 +424,11 @@ fail:
 
 void mbedtls_psa_crypto_free(void)
 {
+    /* Do not try to close a connection that was never started.*/
+    if (handle == -1) {
+        return;
+    }
+
     CLIENT_PRINT("Closing handle");
     psa_close(handle);
     handle = -1;