diff --git a/docs/changes.txt b/docs/changes.txt
index 85541a9e5f..151852f448 100644
--- a/docs/changes.txt
+++ b/docs/changes.txt
@@ -24,6 +24,8 @@ Changes in behaviour not resulting in compilation errors
 - Creating wxBitmap with 0 width or height now always fails in all ports
   (it used to succeed in wxMSW).
 
+- Using invalid flags with wxBoxSizer items now triggers asserts.
+
 Changes in behaviour which may result in build errors
 -----------------------------------------------------
 
diff --git a/include/wx/sizer.h b/include/wx/sizer.h
index 8e7272ab2a..f2c560d788 100644
--- a/include/wx/sizer.h
+++ b/include/wx/sizer.h
@@ -941,6 +941,9 @@ public:
     virtual void RecalcSizes() wxOVERRIDE;
 
 protected:
+    // Only overridden to perform extra debugging checks.
+    virtual wxSizerItem *DoInsert(size_t index, wxSizerItem *item) wxOVERRIDE;
+
     // helpers for our code: this returns the component of the given wxSize in
     // the direction of the sizer and in the other direction, respectively
     int GetSizeInMajorDir(const wxSize& sz) const
diff --git a/src/common/sizer.cpp b/src/common/sizer.cpp
index ccb4f06eb4..21d6eee3ab 100644
--- a/src/common/sizer.cpp
+++ b/src/common/sizer.cpp
@@ -2009,6 +2009,67 @@ void wxFlexGridSizer::RemoveGrowableRow( size_t idx )
 // wxBoxSizer
 //---------------------------------------------------------------------------
 
+wxSizerItem *wxBoxSizer::DoInsert(size_t index, wxSizerItem *item)
+{
+    const int flags = item->GetFlag();
+    if ( IsVertical() )
+    {
+        wxASSERT_MSG
+        (
+            !(flags & wxALIGN_BOTTOM),
+            wxS("Vertical alignment flags are ignored in vertical sizers")
+        );
+
+        // We need to accept wxALIGN_CENTRE_VERTICAL when it is combined with
+        // wxALIGN_CENTRE_HORIZONTAL because this is known as wxALIGN_CENTRE
+        // and we accept it historically in wxSizer API.
+        if ( !(flags & wxALIGN_CENTRE_HORIZONTAL) )
+        {
+            wxASSERT_MSG
+            (
+                !(flags & wxALIGN_CENTRE_VERTICAL),
+                wxS("Vertical alignment flags are ignored in vertical sizers")
+            );
+        }
+
+        if ( flags & wxEXPAND )
+        {
+            wxASSERT_MSG
+            (
+                !(flags & (wxALIGN_RIGHT | wxALIGN_CENTRE_HORIZONTAL)),
+                wxS("Horizontal alignment flags are ignored with wxEXPAND")
+            );
+        }
+    }
+    else // horizontal
+    {
+        wxASSERT_MSG
+        (
+            !(flags & wxALIGN_RIGHT),
+            wxS("Horizontal alignment flags are ignored in horizontal sizers")
+        );
+
+        if ( !(flags & wxALIGN_CENTRE_VERTICAL) )
+        {
+            wxASSERT_MSG
+            (
+                !(flags & wxALIGN_CENTRE_HORIZONTAL),
+                wxS("Horizontal alignment flags are ignored in horizontal sizers")
+            );
+        }
+
+        if ( flags & wxEXPAND )
+        {
+            wxASSERT_MSG(
+                !(flags & (wxALIGN_BOTTOM | wxALIGN_CENTRE_VERTICAL)),
+                wxS("Vertical alignment flags are ignored with wxEXPAND")
+            );
+        }
+    }
+
+    return wxSizer::DoInsert(index, item);
+}
+
 wxSizerItem *wxBoxSizer::AddSpacer(int size)
 {
     return IsVertical() ? Add(0, size) : Add(size, 0);
diff --git a/tests/sizers/boxsizer.cpp b/tests/sizers/boxsizer.cpp
index 75534d2c96..3132c5f061 100644
--- a/tests/sizers/boxsizer.cpp
+++ b/tests/sizers/boxsizer.cpp
@@ -381,7 +381,60 @@ void BoxSizerTestCase::RecalcSizesRespectsMaxSize2()
 
 void BoxSizerTestCase::IncompatibleFlags()
 {
-    WX_ASSERT_FAILS_WITH_ASSERT(
-        m_sizer->Add(10, 10, 0, wxALIGN_BOTTOM | wxALIGN_CENTRE_VERTICAL)
+#define ASSERT_SIZER_INVALID_FLAGS(f, msg) \
+    WX_ASSERT_FAILS_WITH_ASSERT_MESSAGE( \
+            "Expected assertion not generated for " msg, \
+            m_sizer->Add(10, 10, 0, f) \
+        )
+
+#define ASSERT_SIZER_INCOMPATIBLE_FLAGS(f1, f2) \
+    ASSERT_SIZER_INVALID_FLAGS(f1 | f2, \
+        "using incompatible flags " #f1 " and " #f2 \
+    )
+
+    // In horizontal sizers alignment is only used in vertical direction.
+    ASSERT_SIZER_INVALID_FLAGS(
+        wxALIGN_RIGHT,
+        "using wxALIGN_RIGHT in a horizontal sizer"
     );
+
+    ASSERT_SIZER_INVALID_FLAGS(
+        wxALIGN_CENTRE_HORIZONTAL,
+        "using wxALIGN_CENTRE_HORIZONTAL in a horizontal sizer"
+    );
+
+    // However using wxALIGN_CENTRE_HORIZONTAL together with
+    // wxALIGN_CENTRE_VERTICAL as done by wxSizerFlags::Centre() should work.
+    m_sizer->Add(10, 10, wxSizerFlags().Centre());
+
+    // Combining two vertical alignment flags doesn't make sense.
+    ASSERT_SIZER_INCOMPATIBLE_FLAGS(wxALIGN_BOTTOM, wxALIGN_CENTRE_VERTICAL);
+
+    // Combining wxEXPAND with vertical alignment doesn't make sense neither.
+    ASSERT_SIZER_INCOMPATIBLE_FLAGS(wxEXPAND, wxALIGN_CENTRE_VERTICAL);
+    ASSERT_SIZER_INCOMPATIBLE_FLAGS(wxEXPAND, wxALIGN_BOTTOM);
+
+
+    // And now exactly the same thing in the other direction.
+    delete m_sizer;
+    m_sizer = new wxBoxSizer(wxVERTICAL);
+
+    ASSERT_SIZER_INVALID_FLAGS(
+        wxALIGN_BOTTOM,
+        "using wxALIGN_BOTTOM in a vertical sizer"
+    );
+
+    ASSERT_SIZER_INVALID_FLAGS(
+        wxALIGN_CENTRE_VERTICAL,
+        "using wxALIGN_CENTRE_VERTICAL in a vertical sizer"
+    );
+
+    m_sizer->Add(10, 10, wxSizerFlags().Centre());
+
+    ASSERT_SIZER_INCOMPATIBLE_FLAGS(wxALIGN_RIGHT, wxALIGN_CENTRE_HORIZONTAL);
+    ASSERT_SIZER_INCOMPATIBLE_FLAGS(wxEXPAND, wxALIGN_CENTRE_HORIZONTAL);
+    ASSERT_SIZER_INCOMPATIBLE_FLAGS(wxEXPAND, wxALIGN_RIGHT);
+
+#undef ASSERT_SIZER_INCOMPATIBLE_FLAGS
+#undef ASSERT_SIZER_INVALID_FLAGS
 }