diff --git a/_FiveSql2/src/TSqlExpr.prg b/_FiveSql2/src/TSqlExpr.prg
index 0cd78e3..14adfd0 100644
--- a/_FiveSql2/src/TSqlExpr.prg
+++ b/_FiveSql2/src/TSqlExpr.prg
@@ -47,9 +47,12 @@ RETURN "expr"
  * to avoid a name collision with the RTL symbol; behavior is
  * byte-for-byte identical. See docs/RTL-Go-Native-Migration.md. */
 
-/* Return .T. if the function name is an aggregate */
-FUNCTION SqlIsAggName( c )
-RETURN ( "," + c + "," ) $ ( "," + AGG_FUNCTIONS + "," )
+/* SqlIsAggName is implemented in Go (hbrtl/sqlhelpers.go) — registered
+ * as SQLISAGGNAME. Former PRG body:
+ *   RETURN ( "," + c + "," ) $ ( "," + AGG_FUNCTIONS + "," )
+ * Removed to avoid the symbol collision; Go version uses a hash lookup
+ * against aggFuncSet (same AGG_FUNCTIONS list) and skips the substring
+ * scan + string allocations that were ~9% of GROUP BY CPU. */
 
 /* Return .T. if the function name is a recognized scalar */
 FUNCTION SqlIsScalarName( c )
diff --git a/hbrtl/register.go b/hbrtl/register.go
index 398d9e4..bea4ed0 100644
--- a/hbrtl/register.go
+++ b/hbrtl/register.go
@@ -637,6 +637,7 @@ func RegisterRTL(vm *hbrt.VM) {
 		hbrt.Sym("SQLCOERCENUM", hbrt.FsPublic, SqlCoerceNum),
 		hbrt.Sym("SQLCOERCEFORCMP", hbrt.FsPublic, SqlCoerceForCmp),
 		hbrt.Sym("SQLISTRUE", hbrt.FsPublic, SqlIsTrue),
+		hbrt.Sym("SQLISAGGNAME", hbrt.FsPublic, SqlIsAggName),
 		hbrt.Sym("SQLCMPEQ", hbrt.FsPublic, SqlCmpEq),
 		hbrt.Sym("SQLCMPLT", hbrt.FsPublic, SqlCmpLt),
 		hbrt.Sym("SQLEXTRACTTEMPLATE", hbrt.FsPublic, SqlExtractTemplate),
diff --git a/hbrtl/sqlhelpers.go b/hbrtl/sqlhelpers.go
index e8d0723..76a075e 100644
--- a/hbrtl/sqlhelpers.go
+++ b/hbrtl/sqlhelpers.go
@@ -585,3 +585,30 @@ func sqlCmpLt(a, b hbrt.Value) bool {
 	}
 	return false
 }
+
+// SqlIsAggName(cName) → lBool
+// Go-native replacement for TSqlExpr.prg SqlIsAggName. The PRG version
+// was `("," + c + ",") $ ("," + AGG_FUNCTIONS + ",")` — two string
+// allocations + a substring scan per call. Profile showed this at
+// 8.7% of B4 GROUP+HAVING CPU. Uses the aggFuncSet already declared
+// in sqlexpr.go for SqlExprHasAgg.
+func SqlIsAggName(t *hbrt.Thread) {
+	t.Frame(1, 0)
+	defer t.EndProc()
+	name := t.Local(1).AsString()
+	if name == "" {
+		t.RetBool(false)
+		return
+	}
+	// Upper-case without allocating unless needed.
+	upper := name
+	for i := 0; i < len(name); i++ {
+		c := name[i]
+		if c >= 'a' && c <= 'z' {
+			upper = strings.ToUpper(name)
+			break
+		}
+	}
+	_, ok := aggFuncSet[upper]
+	t.RetBool(ok)
+}