diff --git a/include/wx/html/helpctrl.h b/include/wx/html/helpctrl.h
index 6ceaac9f01..a613f8cf3a 100644
--- a/include/wx/html/helpctrl.h
+++ b/include/wx/html/helpctrl.h
@@ -87,7 +87,7 @@ public:
     virtual bool LoadFile(const wxString& file = wxT("")) override;
     virtual bool DisplaySection(int sectionNo) override;
     virtual bool DisplaySection(const wxString& section) override { return Display(section); }
-    virtual bool DisplayBlock(long blockNo) override { return DisplaySection(blockNo); }
+    virtual bool DisplayBlock(long blockNo) override { return DisplaySection(static_cast<int>(blockNo)); }
     virtual bool DisplayTextPopup(const wxString& text, const wxPoint& pos) override;
 
     virtual void SetFrameParameters(const wxString& titleFormat,
diff --git a/include/wx/protocol/protocol.h b/include/wx/protocol/protocol.h
index 2c465ed223..bca2e2c852 100644
--- a/include/wx/protocol/protocol.h
+++ b/include/wx/protocol/protocol.h
@@ -88,7 +88,7 @@ public:
     // override wxSocketBase::SetTimeout function to avoid that the internal
     // m_uiDefaultTimeout goes out-of-sync:
     virtual void SetTimeout(long seconds) override
-        { SetDefaultTimeout(seconds); }
+        { SetDefaultTimeout(static_cast<wxUint32>(seconds)); }
 
 
     // logging support: each wxProtocol object may have the associated logger
diff --git a/include/wx/selstore.h b/include/wx/selstore.h
index 20dee1cd07..290332e640 100644
--- a/include/wx/selstore.h
+++ b/include/wx/selstore.h
@@ -85,8 +85,13 @@ public:
     // return the total number of selected items
     unsigned GetSelectedCount() const
     {
-        return m_defaultState ? m_count - m_itemsSel.GetCount()
-                              : m_itemsSel.GetCount();
+        // we can we never have more than UINT_MAX selected items, knowing that
+        // we store the total number of items in an unsigned m_count, so the
+        // cast is safe.
+        return static_cast<unsigned>(
+                m_defaultState ? m_count - m_itemsSel.GetCount()
+                               : m_itemsSel.GetCount()
+                );
     }
 
     // type of a "cookie" used to preserve the iteration state, this is an
diff --git a/include/wx/string.h b/include/wx/string.h
index 32a313e6d2..b5cc276113 100644
--- a/include/wx/string.h
+++ b/include/wx/string.h
@@ -553,7 +553,7 @@ private:
           c->Reset();
 
           // and remember the last used element
-          LastUsedCacheElement() = c - cacheBegin;
+          LastUsedCacheElement() = static_cast<unsigned int>(c - cacheBegin);
       }
 
       return c;
diff --git a/tests/allheaders.cpp b/tests/allheaders.cpp
index 69ba5e122c..5f8261fd9c 100644
--- a/tests/allheaders.cpp
+++ b/tests/allheaders.cpp
@@ -349,13 +349,14 @@
     GCC_TURN_OFF(padded)
 #endif // gcc >= 4.6
 
-// Do the same for clang too except here we don't bother with the individual
-// warnings and just enable the usual ones because clang mostly includes all
-// the useful warnings in them anyhow.
+// Do the same for clang too except here most of the useful warnings are
+// already included in -Wall, so we just need a few more.
 #ifdef CLANG_TURN_ON
     CLANG_TURN_ON(all)
     CLANG_TURN_ON(extra)
     CLANG_TURN_ON(pedantic)
+
+    CLANG_TURN_ON(shorten-64-to-32)
 #endif // clang