diff --git a/src/mash/Sketch.cpp b/src/mash/Sketch.cpp
index a15d769..f040c23 100644
--- a/src/mash/Sketch.cpp
+++ b/src/mash/Sketch.cpp
@@ -311,6 +311,7 @@ uint64_t Sketch::initParametersFromCapnp(const char * file)
     {
     	setAlphabetFromString(parameters, alphabetNucleotide);
     }
+	munmap(data, fileInfo.st_size);
 	close(fd);
 	
 	try