diff --git a/src/exception.cpp b/src/exception.cpp
index 05647aa..804fab8 100644
--- a/src/exception.cpp
+++ b/src/exception.cpp
@@ -138,7 +138,7 @@
     return EINVAL;
 }
 
-std::string unpackErrorReasonToString(const UnpackErrorReason reason)
+static std::string unpackErrorReasonToString(const UnpackErrorReason reason)
 {
     switch (reason)
     {