--- core/fxcodec/lbmp/fx_bmp.h
+++ core/fxcodec/lbmp/fx_bmp.h
@@ -126,7 +126,7 @@ class BMPDecompressor {
 class CBmpContext : public CCodec_BmpModule::Context {
  public:
   CBmpContext(CCodec_BmpModule* pModule, CCodec_BmpModule::Delegate* pDelegate);
-  ~CBmpContext() override;
+  ~CBmpContext() override {}
 
   BMPDecompressor m_Bmp;
   UnownedPtr<CCodec_BmpModule> const m_pModule;
--- core/fxcrt/string_data_template.h
+++ core/fxcrt/string_data_template.h
@@ -78,7 +78,8 @@
 
   void CopyContentsAt(size_t offset, const CharType* pStr, size_t nLen) {
     ASSERT(offset >= 0 && nLen >= 0 && offset + nLen <= m_nAllocLength);
-    memcpy(m_String + offset, pStr, nLen * sizeof(CharType));
+    if (nLen != 0)
+      memcpy(m_String + offset, pStr, nLen * sizeof(CharType));
     m_String[offset + nLen] = 0;
   }
 
--- core/fxge/cfx_facecache.cpp
+++ core/fxge/cfx_facecache.cpp
@@ -183,7 +183,8 @@ std::unique_ptr<CFX_GlyphBitmap> CFX_FaceCache::RenderGlyph(
       }
     }
   } else {
-    memset(pDestBuf, 0, dest_pitch * bmheight);
+    if (dest_pitch != 0 && bmheight != 0)
+      memset(pDestBuf, 0, dest_pitch * bmheight);
     int rowbytes = std::min(abs(src_pitch), dest_pitch);
     for (int row = 0; row < bmheight; row++)
       memcpy(pDestBuf + row * dest_pitch, pSrcBuf + row * src_pitch, rowbytes);
--- third_party/agg23/agg_rasterizer_scanline_aa.h
+++ third_party/agg23/agg_rasterizer_scanline_aa.h
@@ -349,14 +349,14 @@ public:
                     cover += cur_cell->cover;
                 }
                 if(area) {
-                    alpha = calculate_alpha((cover << (poly_base_shift + 1)) - area, no_smooth);
+                    alpha = calculate_alpha(int(unsigned(cover) << (poly_base_shift + 1)) - area, no_smooth);
                     if(alpha) {
                         sl.add_cell(x, alpha);
                     }
                     x++;
                 }
                 if(num_cells && cur_cell->x > x) {
-                    alpha = calculate_alpha(cover << (poly_base_shift + 1), no_smooth);
+                    alpha = calculate_alpha(unsigned(cover) << (poly_base_shift + 1), no_smooth);
                     if(alpha) {
                         sl.add_span(x, cur_cell->x - x, alpha);
                     }