diff --git a/src/cmd/compile/internal/types2/builtins.go b/src/cmd/compile/internal/types2/builtins.go
index d4463bc4b09..549d94615bc 100644
--- a/src/cmd/compile/internal/types2/builtins.go
+++ b/src/cmd/compile/internal/types2/builtins.go
@@ -91,6 +91,17 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 		// to type []byte with a second argument of string type followed by ... .
 		// This form appends the bytes of the string."
 
+		// In either case, the first argument must be a slice; in particular it
+		// cannot be the predeclared nil value. Note that nil is not excluded by
+		// the assignability requirement alone for the special case (go.dev/issue/76220).
+		// spec: "If S is a type parameter, all types in its type set
+		// must have the same underlying slice type []E."
+		E, err := sliceElem(x)
+		if err != nil {
+			check.errorf(x, InvalidAppend, "invalid append: %s", err.format(check))
+			return
+		}
+
 		// Handle append(bytes, y...) special case, where
 		// the type set of y is {string} or {string, []byte}.
 		var sig *Signature
@@ -119,13 +130,6 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 
 		// general case
 		if sig == nil {
-			// spec: "If S is a type parameter, all types in its type set
-			// must have the same underlying slice type []E."
-			E, err := sliceElem(x)
-			if err != nil {
-				check.errorf(x, InvalidAppend, "invalid append: %s", err.format(check))
-				return
-			}
 			// check arguments by creating custom signature
 			sig = makeSig(x.typ, x.typ, NewSlice(E)) // []E required for variadic signature
 			sig.variadic = true
diff --git a/src/go/types/builtins.go b/src/go/types/builtins.go
index 04d294db0c1..90a3b4a901f 100644
--- a/src/go/types/builtins.go
+++ b/src/go/types/builtins.go
@@ -94,6 +94,17 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 		// to type []byte with a second argument of string type followed by ... .
 		// This form appends the bytes of the string."
 
+		// In either case, the first argument must be a slice; in particular it
+		// cannot be the predeclared nil value. Note that nil is not excluded by
+		// the assignability requirement alone for the special case (go.dev/issue/76220).
+		// spec: "If S is a type parameter, all types in its type set
+		// must have the same underlying slice type []E."
+		E, err := sliceElem(x)
+		if err != nil {
+			check.errorf(x, InvalidAppend, "invalid append: %s", err.format(check))
+			return
+		}
+
 		// Handle append(bytes, y...) special case, where
 		// the type set of y is {string} or {string, []byte}.
 		var sig *Signature
@@ -122,13 +133,6 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 
 		// general case
 		if sig == nil {
-			// spec: "If S is a type parameter, all types in its type set
-			// must have the same underlying slice type []E."
-			E, err := sliceElem(x)
-			if err != nil {
-				check.errorf(x, InvalidAppend, "invalid append: %s", err.format(check))
-				return
-			}
 			// check arguments by creating custom signature
 			sig = makeSig(x.typ, x.typ, NewSlice(E)) // []E required for variadic signature
 			sig.variadic = true
diff --git a/src/internal/types/testdata/fixedbugs/issue76220.go b/src/internal/types/testdata/fixedbugs/issue76220.go
new file mode 100644
index 00000000000..ad465010a05
--- /dev/null
+++ b/src/internal/types/testdata/fixedbugs/issue76220.go
@@ -0,0 +1,17 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+func _() {
+	append(nil /* ERROR "argument must be a slice; have untyped nil" */, ""...)
+}
+
+// test case from issue
+
+func main() {
+	s := "hello"
+	msg := append(nil /* ERROR "argument must be a slice; have untyped nil" */, s...)
+	print(msg)
+}