diff --git a/src/libutil/source-accessor.cc b/src/libutil/source-accessor.cc
index 66093d2cc..e797951c7 100644
--- a/src/libutil/source-accessor.cc
+++ b/src/libutil/source-accessor.cc
@@ -53,7 +53,7 @@ SourceAccessor::Stat SourceAccessor::lstat(const CanonPath & path)
     if (auto st = maybeLstat(path))
         return *st;
     else
-        throw Error("path '%s' does not exist", showPath(path));
+        throw FileNotFound("path '%s' does not exist", showPath(path));
 }
 
 void SourceAccessor::setPathDisplay(std::string displayPrefix, std::string displaySuffix)
diff --git a/src/libutil/source-accessor.hh b/src/libutil/source-accessor.hh
index d7fb0af5f..cc8db01f5 100644
--- a/src/libutil/source-accessor.hh
+++ b/src/libutil/source-accessor.hh
@@ -29,6 +29,8 @@ enum class SymlinkResolution {
     Full,
 };
 
+MakeError(FileNotFound, Error);
+
 /**
  * A read-only filesystem abstraction. This is used by the Nix
  * evaluator and elsewhere for accessing sources in various