diff --git a/proton/session/exceptions.py b/proton/session/exceptions.py
index 0a6784f..4171b5e 100644
--- a/proton/session/exceptions.py
+++ b/proton/session/exceptions.py
@@ -33,6 +33,11 @@ class ProtonCryptoError(ProtonError):
     In general this has to be handled as being fatal, as something is super-wrong."""
 
 
+class ProtonCryptoPasswordTooLongError(ProtonCryptoError):
+    """Exception raised when the password exceeds bcrypt's 72-byte limit.
+    The user should shorten their password to at most 72 bytes."""
+
+
 class ProtonUnsupportedAuthVersionError(ProtonCryptoError):
     """When the auth_version returned by the API is lower then what is currently supported.
     This is usually fixed with a login via the webclient."""
diff --git a/proton/session/srp/util.py b/proton/session/srp/util.py
index cedf655..c98d6bc 100644
--- a/proton/session/srp/util.py
+++ b/proton/session/srp/util.py
@@ -20,7 +20,7 @@
 import bcrypt
 import os
 
-from proton.session.exceptions import ProtonUnsupportedAuthVersionError
+from proton.session.exceptions import ProtonUnsupportedAuthVersionError, ProtonCryptoPasswordTooLongError
 
 
 PM_VERSION = 4
@@ -39,7 +39,13 @@ def bcrypt_b64_encode(s):  # The joy of bcrypt
 def hash_password_3(hash_class, password, salt, modulus):
     salt = (salt + b"proton")[:16]
     salt = bcrypt_b64_encode(salt)[:22]
-    hashed = bcrypt.hashpw(password, b"$2y$10$" + salt)
+    try:
+        hashed = bcrypt.hashpw(password, b"$2y$10$" + salt)
+    except ValueError as e:
+        raise ProtonCryptoPasswordTooLongError(
+            "Password exceeds bcrypt's 72-byte limit. "
+            "Please shorten your password to at most 72 bytes."
+        ) from e
     return hash_class(hashed + modulus).digest()