diff --git a/include/ctrff/pica.hpp b/include/ctrff/pica.hpp
index 2ff17df..d9b3a61 100644
--- a/include/ctrff/pica.hpp
+++ b/include/ctrff/pica.hpp
@@ -25,10 +25,10 @@ enum Color : u32 {
   A4,  // tested
 };
 CTRFF_API void EncodeImage(std::vector<ctrff::u8>& ret,
-                           std::vector<ctrff::u8> rgba, int w, int h,
+                           const std::vector<ctrff::u8>& rgba, int w, int h,
                            Color dst);
 CTRFF_API void DecodeImage(std::vector<ctrff::u8>& ret,
-                           std::vector<ctrff::u8> pixels, int w, int h,
+                           const std::vector<ctrff::u8>& pixels, int w, int h,
                            Color src);
 }  // namespace Pica
 }  // namespace ctrff
\ No newline at end of file
diff --git a/source/pica.cpp b/source/pica.cpp
index 4e883c0..ac02860 100644
--- a/source/pica.cpp
+++ b/source/pica.cpp
@@ -4,7 +4,7 @@
 namespace ctrff {
 namespace Pica {
 CTRFF_API void EncodeImage(std::vector<ctrff::u8>& ret,
-                           std::vector<ctrff::u8> rgba, int w, int h,
+                           const std::vector<ctrff::u8>& rgba, int w, int h,
                            Color dst_color) {
   // Only used in rgb/rgba
   int bpp = dst_color == RGBA8888 ? 4 : 3;
@@ -152,7 +152,7 @@ CTRFF_API void EncodeImage(std::vector<ctrff::u8>& ret,
 }
 
 CTRFF_API void DecodeImage(std::vector<ctrff::u8>& ret,
-                           std::vector<ctrff::u8> pixels, int w, int h,
+                           const std::vector<ctrff::u8>& pixels, int w, int h,
                            Color src_color) {
   switch (src_color) {
     case RGB565: