diff --git a/src/Images.jl b/src/Images.jl
index 649a20eb..0a8b72c8 100644
--- a/src/Images.jl
+++ b/src/Images.jl
@@ -57,7 +57,7 @@ const is_little_endian = ENDIAN_BOM == 0x04030201
 @reexport using ImageQualityIndexes
 
 # StatsBase also exports psnr
-psnr = ImageQualityIndexes.psnr
+const psnr = ImageQualityIndexes.psnr
 export psnr
 
 # Both ImageMetadata v0.9.0 and ImageAxes v0.6.0 deprecate the symbol data and