diff --git a/device_memory.cpp b/device_memory.cpp
index 26dd871..7d18d87 100644
--- a/device_memory.cpp
+++ b/device_memory.cpp
@@ -39,7 +39,7 @@ cruft::vk::map_t::destroy (device &_device, device_memory &_memory)
 
     vkUnmapMemory (_device.native (), _memory.native ());
 
-    *this = {nullptr, nullptr};
+    *this = nullptr;
 }
 
 
diff --git a/pipeline_cache.cpp b/pipeline_cache.cpp
index d4f0c6b..469931a 100644
--- a/pipeline_cache.cpp
+++ b/pipeline_cache.cpp
@@ -19,6 +19,8 @@
 
 #include "./device.hpp"
 
+#include <cruft/util/cast.hpp>
+
 using cruft::vk::pipeline_cache;
 
 
@@ -28,7 +30,8 @@ pipeline_cache::merge (const device &dev,
                        const pipeline_cache *first,
                        const pipeline_cache *last)
 {
-    auto err = vkMergePipelineCaches (dev.native (), native (), last - first, &first->native ());
+    CHECK_GE (last, first);
+    auto err = vkMergePipelineCaches (dev.native (), native (), trunc_cast<uint32_t> (last - first), &first->native ());
     error::try_code (err);
 }