diff --git a/drivers/BusIn.cpp b/drivers/BusIn.cpp
index f6cc933e7e..c14351f3fe 100644
--- a/drivers/BusIn.cpp
+++ b/drivers/BusIn.cpp
@@ -97,7 +97,7 @@ BusIn::operator int()
 DigitalIn &BusIn::operator[](int index)
 {
     // No lock needed since _pin is not modified outside the constructor
-    MBED_ASSERT(index >= 0 && index <= 16);
+    MBED_ASSERT(index >= 0 && index < 16);
     MBED_ASSERT(_pin[index]);
     return *_pin[index];
 }
diff --git a/drivers/BusInOut.cpp b/drivers/BusInOut.cpp
index 950cbb5d58..170e035b96 100644
--- a/drivers/BusInOut.cpp
+++ b/drivers/BusInOut.cpp
@@ -128,7 +128,7 @@ BusInOut &BusInOut::operator= (BusInOut &rhs)
 DigitalInOut &BusInOut::operator[](int index)
 {
     // No lock needed since _pin is not modified outside the constructor
-    MBED_ASSERT(index >= 0 && index <= 16);
+    MBED_ASSERT(index >= 0 && index < 16);
     MBED_ASSERT(_pin[index]);
     return *_pin[index];
 }
diff --git a/drivers/BusOut.cpp b/drivers/BusOut.cpp
index 913ba19750..769d2e6891 100644
--- a/drivers/BusOut.cpp
+++ b/drivers/BusOut.cpp
@@ -95,7 +95,7 @@ BusOut &BusOut::operator= (BusOut &rhs)
 DigitalOut &BusOut::operator[](int index)
 {
     // No lock needed since _pin is not modified outside the constructor
-    MBED_ASSERT(index >= 0 && index <= 16);
+    MBED_ASSERT(index >= 0 && index < 16);
     MBED_ASSERT(_pin[index]);
     return *_pin[index];
 }