diff --git a/core/jni/android/graphics/Bitmap.cpp b/core/jni/android/graphics/Bitmap.cpp
index 5a74a2473b320..b085bc93f5dde 100755
--- a/core/jni/android/graphics/Bitmap.cpp
+++ b/core/jni/android/graphics/Bitmap.cpp
@@ -48,7 +48,7 @@ namespace android {
 
 class BitmapWrapper {
 public:
-    BitmapWrapper(Bitmap* bitmap)
+    explicit BitmapWrapper(Bitmap* bitmap)
         : mBitmap(bitmap) { }
 
     void freePixels() {
diff --git a/core/jni/android/graphics/FontUtils.h b/core/jni/android/graphics/FontUtils.h
index 9eaaa4964b66d..30fdf2478887b 100644
--- a/core/jni/android/graphics/FontUtils.h
+++ b/core/jni/android/graphics/FontUtils.h
@@ -27,7 +27,7 @@ class FontFamily;
 namespace android {
 
 struct FontFamilyWrapper {
-  FontFamilyWrapper(std::shared_ptr<minikin::FontFamily>&& family) : family(family) {}
+  explicit FontFamilyWrapper(std::shared_ptr<minikin::FontFamily>&& family) : family(family) {}
   std::shared_ptr<minikin::FontFamily> family;
 };
 
diff --git a/core/jni/android/graphics/GIFMovie.cpp b/core/jni/android/graphics/GIFMovie.cpp
index dd99b377988ff..f84a4bd09073d 100644
--- a/core/jni/android/graphics/GIFMovie.cpp
+++ b/core/jni/android/graphics/GIFMovie.cpp
@@ -21,7 +21,7 @@
 
 class GIFMovie : public Movie {
 public:
-    GIFMovie(SkStream* stream);
+    explicit GIFMovie(SkStream* stream);
     virtual ~GIFMovie();
 
 protected:
diff --git a/core/jni/fd_utils.cpp b/core/jni/fd_utils.cpp
index a03e929fa60be..d8d919df6c245 100644
--- a/core/jni/fd_utils.cpp
+++ b/core/jni/fd_utils.cpp
@@ -148,7 +148,7 @@ class FileDescriptorInfo {
   const bool is_sock;
 
  private:
-  FileDescriptorInfo(int fd);
+  explicit FileDescriptorInfo(int fd);
 
   FileDescriptorInfo(struct stat stat, const std::string& file_path, int fd, int open_flags,
                      int fd_flags, int fs_flags, off_t offset);
diff --git a/core/jni/fd_utils.h b/core/jni/fd_utils.h
index a3570d7ed1fba..09022a2e24086 100644
--- a/core/jni/fd_utils.h
+++ b/core/jni/fd_utils.h
@@ -86,7 +86,7 @@ class FileDescriptorTable {
   bool ReopenOrDetach(std::string* error_msg);
 
  private:
-  FileDescriptorTable(const std::unordered_map<int, FileDescriptorInfo*>& map);
+  explicit FileDescriptorTable(const std::unordered_map<int, FileDescriptorInfo*>& map);
 
   bool RestatInternal(std::set<int>& open_fds, std::string* error_msg);