diff --git a/Grbl_Esp32/src/Pins/GPIOPinDetail.cpp b/Grbl_Esp32/src/Pins/GPIOPinDetail.cpp
index 9cebe6c9..ecf29c44 100644
--- a/Grbl_Esp32/src/Pins/GPIOPinDetail.cpp
+++ b/Grbl_Esp32/src/Pins/GPIOPinDetail.cpp
@@ -104,7 +104,8 @@ namespace Pins {
         // that were allocated by the constructor up to that point _MUST_ be freed! Otherwise, you
         // WILL get into trouble.
 
-        Assert(_capabilities != PinCapabilities::None, "Bad GPIO number");
+        Assert(index < nGPIOPins, "Pin number is greater than max %d", nGPIOPins - 1);
+        Assert(_capabilities != PinCapabilities::None, "Unavailable GPIO");
         Assert(!_claimed[index], "Pin is already used.");
 
         // User defined pin capabilities
diff --git a/Grbl_Esp32/src/Pins/I2SOPinDetail.cpp b/Grbl_Esp32/src/Pins/I2SOPinDetail.cpp
index 2433f40c..51cab9d1 100644
--- a/Grbl_Esp32/src/Pins/I2SOPinDetail.cpp
+++ b/Grbl_Esp32/src/Pins/I2SOPinDetail.cpp
@@ -30,6 +30,7 @@ namespace Pins {
     I2SOPinDetail::I2SOPinDetail(uint8_t index, const PinOptionsParser& options) :
         PinDetail(index), _capabilities(PinCapabilities::Output | PinCapabilities::I2S), _attributes(Pins::PinAttributes::Undefined),
         _readWriteMask(0) {
+        Assert(index < nI2SOPins, "Pin number is greater than max %d", nI2SOPins - 1);
         Assert(!_claimed[index], "Pin is already used.");
         // User defined pin capabilities
         for (auto opt : options) {