diff --git a/encode_vm.go b/encode_vm.go
index 0bc3cc5..7a08dd3 100644
--- a/encode_vm.go
+++ b/encode_vm.go
@@ -51,7 +51,7 @@ func errMarshaler(code *opcode, err error) *MarshalerError {
 
 func (e *Encoder) run(ctx *encodeRuntimeContext, b []byte, code *opcode) ([]byte, error) {
 	recursiveLevel := 0
-	seenPtr := map[uintptr]struct{}{}
+	var seenPtr map[uintptr]struct{}
 	ptrOffset := uintptr(0)
 	ctxptr := ctx.ptr()
 
@@ -211,6 +211,9 @@ func (e *Encoder) run(ctx *encodeRuntimeContext, b []byte, code *opcode) ([]byte
 				code = code.next
 				break
 			}
+			if seenPtr == nil {
+				seenPtr = map[uintptr]struct{}{}
+			}
 			if _, exists := seenPtr[ptr]; exists {
 				return nil, errUnsupportedValue(code, ptr)
 			}
@@ -288,6 +291,9 @@ func (e *Encoder) run(ctx *encodeRuntimeContext, b []byte, code *opcode) ([]byte
 				code = code.next
 				break
 			}
+			if seenPtr == nil {
+				seenPtr = map[uintptr]struct{}{}
+			}
 			if _, exists := seenPtr[ptr]; exists {
 				return nil, errUnsupportedValue(code, ptr)
 			}
@@ -992,6 +998,9 @@ func (e *Encoder) run(ctx *encodeRuntimeContext, b []byte, code *opcode) ([]byte
 					}
 				}
 			}
+			if seenPtr == nil {
+				seenPtr = map[uintptr]struct{}{}
+			}
 			seenPtr[ptr] = struct{}{}
 			c := code.jmp.code
 			c.end.next = newEndOp(&encodeCompileContext{})