diff --git a/rdflib/namespace.py b/rdflib/namespace.py
index fc7985fa4..8228a0e03 100644
--- a/rdflib/namespace.py
+++ b/rdflib/namespace.py
@@ -798,6 +798,9 @@ def bind(self, prefix, namespace, override=True, replace=False):
         # When documenting explain that override only applies in what cases
         if prefix is None:
             prefix = ""
+        elif " " in prefix:
+            raise KeyError("Prefixes may not contain spaces.")
+            
         bound_namespace = self.store.namespace(prefix)
         # Check if the bound_namespace contains a URI
         # and if so convert it into a URIRef for comparison