diff --git a/rust/ql/lib/codeql/files/FileSystem.qll b/rust/ql/lib/codeql/files/FileSystem.qll
index cfab33b9a440..93ff7be604e0 100644
--- a/rust/ql/lib/codeql/files/FileSystem.qll
+++ b/rust/ql/lib/codeql/files/FileSystem.qll
@@ -45,13 +45,16 @@ extensible predicate additionalExternalFile(string relativePath);
 
 /** A file. */
 class File extends Container, Impl::File {
+  pragma[nomagic]
+  private predicate isAdditionalExternalFile() { additionalExternalFile(this.getRelativePath()) }
+
   /**
    * Holds if this file was extracted from the source code of the target project
    * (rather than another location such as inside a dependency).
    */
   predicate fromSource() {
     exists(ExtractorStep s | s.getAction() = "Extract" and s.getFile() = this) and
-    not additionalExternalFile(this.getRelativePath())
+    not this.isAdditionalExternalFile()
   }
 
   /**