diff --git a/src/libfetchers/filtering-source-accessor.cc b/src/libfetchers/filtering-source-accessor.cc
index dfd9e536d..d4557b6d4 100644
--- a/src/libfetchers/filtering-source-accessor.cc
+++ b/src/libfetchers/filtering-source-accessor.cc
@@ -2,6 +2,12 @@
 
 namespace nix {
 
+std::optional<std::filesystem::path> FilteringSourceAccessor::getPhysicalPath(const CanonPath & path)
+{
+    checkAccess(path);
+    return next->getPhysicalPath(prefix / path);
+}
+
 std::string FilteringSourceAccessor::readFile(const CanonPath & path)
 {
     checkAccess(path);
diff --git a/src/libfetchers/filtering-source-accessor.hh b/src/libfetchers/filtering-source-accessor.hh
index 9ec7bc21f..1f8d84e53 100644
--- a/src/libfetchers/filtering-source-accessor.hh
+++ b/src/libfetchers/filtering-source-accessor.hh
@@ -30,6 +30,8 @@ struct FilteringSourceAccessor : SourceAccessor
         displayPrefix.clear();
     }
 
+    std::optional<std::filesystem::path> getPhysicalPath(const CanonPath & path) override;
+
     std::string readFile(const CanonPath & path) override;
 
     bool pathExists(const CanonPath & path) override;