diff --git a/src/main/java/intellij_awk/psi/AwkStringMixin.java b/src/main/java/intellij_awk/psi/AwkStringMixin.java
index 0e643c0..180b671 100644
--- a/src/main/java/intellij_awk/psi/AwkStringMixin.java
+++ b/src/main/java/intellij_awk/psi/AwkStringMixin.java
@@ -21,27 +21,43 @@ public AwkStringMixin(@NotNull ASTNode node) {
   private static final Pattern stringThatCanBeFunctionName =
       Pattern.compile("\"[A-Za-z_][A-Za-z0-9_]*\"");
 
-  static boolean canBeFunctionName(String s) {
-    return stringThatCanBeFunctionName.matcher(s).matches();
-  }
-
   @Override
   public String getName() {
+    return getPossibleFunctionName();
+  }
+
+  @Nullable
+  private String getPossibleFunctionName() {
     String str = getText();
     return canBeFunctionName(str) ? unquoteString(str) : null;
   }
 
+  static boolean canBeFunctionName(String s) {
+    return stringThatCanBeFunctionName.matcher(s).matches();
+  }
+
   public PsiElement setName(String newName) {
     return replaceNameNode(AwkElementFactory.createFunctionCallName(getProject(), newName));
   }
 
   @Override
   public PsiReference getReference() {
-    return getName() != null && isRhsOfAssignment()
+    return getPossibleFunctionName() != null && canBeFunctionReference()
         ? new AwkReferenceFunction(this, TextRange.from(1, getTextLength() - 2))
         : null;
   }
 
+  private boolean canBeFunctionReference() {
+    return isRhsOfAssignment() || isUserFunctionArgument();
+  }
+
+  /** `f("fname")` but not `substr("fname")` (built-in) */
+  private boolean isUserFunctionArgument() {
+    AwkGawkFuncCallList callList = AwkUtil.findParent(this, AwkGawkFuncCallList.class);
+    return callList != null && callList.getParent() instanceof AwkFunctionCallUser;
+  }
+
+  /** `a = "fname"` */
   private boolean isRhsOfAssignment() {
     return AwkUtil.isType(AwkUtil.getPrevNotWhitespace(getParent()), AwkTypes.ASSIGN);
   }