diff --git a/ChangeLog.d/fix_ubsan_mp_aead_gcm.txt b/ChangeLog.d/fix_ubsan_mp_aead_gcm.txt
new file mode 100644
index 0000000..e4726a4
--- /dev/null
+++ b/ChangeLog.d/fix_ubsan_mp_aead_gcm.txt
@@ -0,0 +1,3 @@
+Bugfix
+   * Fix undefined behaviour (incrementing a NULL pointer by zero length) when
+     passing in zero length additional data to multipart AEAD.
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 969c695..0a9011a 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -5194,6 +5194,12 @@
         goto exit;
     }
 
+    /* No input to add (zero length), nothing to do. */
+    if (input_length == 0) {
+        status = PSA_SUCCESS;
+        goto exit;
+    }
+
     if (operation->lengths_set) {
         if (operation->ad_remaining < input_length) {
             status = PSA_ERROR_INVALID_ARGUMENT;