diff --git a/FlexCAN.cpp b/FlexCAN.cpp
index 2033284..1aef1fb 100644
--- a/FlexCAN.cpp
+++ b/FlexCAN.cpp
@@ -22,6 +22,7 @@
 #define FLEXCANb_IDFLT_TAB(b, n)          (*(vuint32_t*)(b+0xE0+(n*4)))
 #define FLEXCANb_MB_MASK(b, n)            (*(vuint32_t*)(b+0x880+(n*4)))
 #define FLEXCANb_ESR1(b)                  (*(vuint32_t*)(b+0x20))
+#define FLEXCANb_CTRL2(b)                 (*(vuint32_t*)(b+0x34))
 
 #if defined(__MK66FX1M0__)
 # define INCLUDE_FLEXCAN_CAN1
@@ -216,6 +217,9 @@ void FlexCAN::begin (uint32_t baud, const CAN_filter_t &mask, uint8_t txAlt, uin
 
     setBaudRate(baud);
 
+    // need to modify CTRL2 to allow extended frames, even if global mailbox filter is unused
+    FLEXCANb_CTRL2(flexcanBase) |= (BIT16); 
+
     // enable per-mailbox filtering
 
     FLEXCANb_MCR(flexcanBase) |= FLEXCAN_MCR_IRMQ;