diff --git a/lib/rdf/repository.rb b/lib/rdf/repository.rb
index e9efc817..2d1f4fb3 100644
--- a/lib/rdf/repository.rb
+++ b/lib/rdf/repository.rb
@@ -124,16 +124,18 @@ def initialize(uri: nil, title: nil, **options, &block)
     ##
     # Returns `true` if this respository supports the given `feature`.
     #
-    # Supported features include those from {RDF::Enumerable#supports?} along with the following:
-    #   * `:transactions` supports atomic transactions
-    #   * `:snapshots` supports creation of immutable snapshots of current contents via #snapshot.
+    # Supported features include those from {RDF::Enumerable#supports?} along 
+    #  with the following:
+    #   * `:atomic_write` supports atomic write in transaction scopes
+    #   * `:snapshots` supports creation of immutable snapshots of current 
+    #        contents via #snapshot.
     # @see RDF::Enumerable#supports?
     def supports?(feature)
       case feature.to_sym
       when :graph_name   then @options[:with_graph_name]
       when :inference    then false  # forward-chaining inference
       when :validity     then @options.fetch(:with_validity, true)
-      when :transactions then false
+      when :atomic_write then false
       when :snapshots    then false
       else false
       end
@@ -272,7 +274,7 @@ def supports?(feature)
         when :graph_name   then @options[:with_graph_name]
         when :inference    then false  # forward-chaining inference
         when :validity     then @options.fetch(:with_validity, true)
-        when :transactions then true
+        when :atomic_write then true
         when :snapshots    then true
         else false
         end
diff --git a/lib/rdf/transaction.rb b/lib/rdf/transaction.rb
index f0021a0c..a4dc8a8c 100644
--- a/lib/rdf/transaction.rb
+++ b/lib/rdf/transaction.rb
@@ -6,7 +6,7 @@ module RDF
   #
   # Repository implementations may provide support for transactional updates
   # by providing an atomic implementation of {Mutable#apply_changeset} and 
-  # responding to `#supports?(:transactions)` with `true`.
+  # responding to `#supports?(:atomic_write)` with `true`.
   # 
   # We carefully distinguish between read-only and read/write transactions,
   # in order to enable repository implementations to take out the
@@ -18,7 +18,7 @@ module RDF
   # transaction's scope. In case repository implementations should be unable
   # to provide full ACID guarantees for transactions, that must be clearly 
   # indicated in their documentation. If update atomicity is not provided, 
-  # `#supports?(:transactions)` must respond `false`.
+  # `#supports?(:atomic_write)` must respond `false`.
   #
   # @example Executing a read-only transaction
   #   repository = RDF::Repository.new
@@ -145,7 +145,11 @@ def initialize(repository, mutable: false, **options, &block)
         repository.supports?(:snapshots) ? repository.snapshot : repository
       @options  = options.dup
       @mutable  = mutable
-      
+
+      raise TransactionError, 
+            'Tried to open a mutable transaction on an immutable repository' if
+        @mutable && !@repository.mutable?
+
       @changes = RDF::Changeset.new
       
       if block_given?
diff --git a/spec/model_graph_spec.rb b/spec/model_graph_spec.rb
index 70739ec6..5eadaa92 100644
--- a/spec/model_graph_spec.rb
+++ b/spec/model_graph_spec.rb
@@ -171,6 +171,10 @@
     it_behaves_like 'an RDF::Queryable'
   end
 
+  context 'transactions' do
+    it { require 'pry'; binding.pry }
+  end
+
   context "Examples" do
     let(:graph) {described_class.new}