diff --git a/mcmc/mcmc_cholesky_vertex.py b/mcmc/mcmc_cholesky_vertex.py
index f20d2a3..25992f9 100644
--- a/mcmc/mcmc_cholesky_vertex.py
+++ b/mcmc/mcmc_cholesky_vertex.py
@@ -77,8 +77,8 @@ def get_binary_start_type(self) -> ExecutableType:
 
     @overrides(
         AbstractGeneratesDataSpecification.generate_data_specification)
-    def generate_data_specification(
-            self, spec: DataSpecificationGenerator, placement: Placement):
+    def generate_data_specification(self, spec: DataSpecificationGenerator,
+                                    placement: Placement) -> None:
 
         # Reserve and write the parameters region
         spec.reserve_memory_region(
diff --git a/mcmc/mcmc_coordinator_vertex.py b/mcmc/mcmc_coordinator_vertex.py
index f788181..0b89246 100644
--- a/mcmc/mcmc_coordinator_vertex.py
+++ b/mcmc/mcmc_coordinator_vertex.py
@@ -207,8 +207,8 @@ def get_binary_start_type(self) -> ExecutableType:
 
     @overrides(
         AbstractGeneratesDataSpecification.generate_data_specification)
-    def generate_data_specification(
-            self, spec: DataSpecificationGenerator, placement: Placement):
+    def generate_data_specification(self, spec: DataSpecificationGenerator,
+                                    placement: Placement) -> None:
         routing_info = FecDataView.get_routing_infos()
 
         # Reserve and write the parameters region
diff --git a/mcmc/mcmc_root_finder_vertex.py b/mcmc/mcmc_root_finder_vertex.py
index 97d490b..0d43e4a 100644
--- a/mcmc/mcmc_root_finder_vertex.py
+++ b/mcmc/mcmc_root_finder_vertex.py
@@ -76,8 +76,8 @@ def get_binary_start_type(self) -> ExecutableType:
 
     @overrides(
         AbstractGeneratesDataSpecification.generate_data_specification)
-    def generate_data_specification(
-            self, spec: DataSpecificationGenerator, placement: Placement):
+    def generate_data_specification(self, spec: DataSpecificationGenerator,
+                                    placement: Placement) -> None:
 
         # Reserve and write the parameters region
         spec.reserve_memory_region(
diff --git a/mcmc/mcmc_vertex.py b/mcmc/mcmc_vertex.py
index 74262a1..68cf2b7 100644
--- a/mcmc/mcmc_vertex.py
+++ b/mcmc/mcmc_vertex.py
@@ -211,8 +211,8 @@ def get_binary_start_type(self) -> ExecutableType:
 
     @overrides(
         AbstractGeneratesDataSpecification.generate_data_specification)
-    def generate_data_specification(
-            self, spec: DataSpecificationGenerator, placement: Placement):
+    def generate_data_specification(self, spec: DataSpecificationGenerator,
+                                    placement: Placement) -> None:
 
         routing_info = FecDataView.get_routing_infos()
         # Reserve and write the recording regions