diff --git a/src/libexpr/eval-inline.hh b/src/libexpr/eval-inline.hh
index b470fa315..0748fbd3f 100644
--- a/src/libexpr/eval-inline.hh
+++ b/src/libexpr/eval-inline.hh
@@ -78,15 +78,4 @@ inline void EvalState::forceList(Value & v, const Pos & pos)
         throwTypeError("value is %1% while a list was expected, at %2%", v, pos);
 }
 
-inline bool EvalState::isFunctor(Value& fun)
-{
-    if (fun.type == tAttrs) {
-      auto found = fun.attrs->find(sFunctor);
-      if (found != fun.attrs->end()) {
-        return true;
-      }
-    }
-    return false;
-}
-
 }
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 93c3111af..fb96e8b4d 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -1291,6 +1291,12 @@ bool EvalState::forceBool(Value & v)
 }
 
 
+bool EvalState::isFunctor(Value & fun)
+{
+    return fun.type == tAttrs && fun.attrs->find(sFunctor) != fun.attrs->end();
+}
+
+
 void EvalState::forceFunction(Value & v, const Pos & pos)
 {
     forceValue(v);