diff --git a/I2CManager.cpp b/I2CManager.cpp
index 6d5db41..aad6418 100644
--- a/I2CManager.cpp
+++ b/I2CManager.cpp
@@ -72,18 +72,23 @@ static const FSH * guessI2CDeviceType(uint8_t address) {
 void I2CManagerClass::begin(void) {
   if (!_beginCompleted) {
     _beginCompleted = true;
+
+    // Check for short-circuit or floating lines (no pull-up) on I2C before enabling I2C
+    const FSH *message = F("WARNING: Possible short-circuit or inadequate pullup on I2C %S line");
+    pinMode(SDA, INPUT);
+    if (!digitalRead(SDA))
+      DIAG(message, F("SDA"));
+    pinMode(SCL, INPUT);
+    if (!digitalRead(SCL))
+      DIAG(message, F("SCL"));
+
+    // Now initialise I2C
     _initialise();
 
     #if defined(I2C_USE_WIRE)
     DIAG(F("I2CManager: Using Wire library"));
     #endif
 
-    // Check for short-circuits on I2C
-    if (!digitalRead(SDA))
-      DIAG(F("WARNING: Possible short-circuit on I2C SDA line"));
-    if (!digitalRead(SCL))
-      DIAG(F("WARNING: Possible short-circuit on I2C SCL line"));
-
     // Probe and list devices.  Use standard mode 
     //  (clock speed 100kHz) for best device compatibility.
     _setClock(100000);