diff --git a/OLEDDisplay.cpp b/OLEDDisplay.cpp
index 9caf84f..5c0e05f 100644
--- a/OLEDDisplay.cpp
+++ b/OLEDDisplay.cpp
@@ -563,7 +563,7 @@ void OLEDDisplay::normalDisplay(void) {
   sendCommand(NORMALDISPLAY);
 }
 
-void OLEDDisplay::setContrast(char contrast, char precharge, char comdetect) {
+void OLEDDisplay::setContrast(uint8_t contrast, uint8_t precharge, uint8_t comdetect) {
   sendCommand(SETPRECHARGE); //0xD9
   sendCommand(precharge); //0xF1 default, to lower the contrast, put 1-1F
   sendCommand(SETCONTRAST);
@@ -854,4 +854,4 @@ char* OLEDDisplay::utf8ascii(String str) {
 
 void OLEDDisplay::setFontTableLookupFunction(FontTableLookupFunction function) {
   this->fontTableLookupFunction = function;
-}
\ No newline at end of file
+}
diff --git a/OLEDDisplay.h b/OLEDDisplay.h
index 9326323..5141d73 100644
--- a/OLEDDisplay.h
+++ b/OLEDDisplay.h
@@ -217,7 +217,7 @@ class OLEDDisplay : public Print {
     // Set display contrast
     // really low brightness & contrast: contrast = 10, precharge = 5, comdetect = 0
     // normal brightness & contrast:  contrast = 100
-    void setContrast(char contrast, char precharge = 241, char comdetect = 64);
+    void setContrast(uint8_t contrast, uint8_t precharge = 241, uint8_t comdetect = 64);
 
     // Reset display rotation or mirroring
     void resetOrientation();
diff --git a/UPGRADE-4.0.md b/UPGRADE-4.0.md
index 1d371c5..4b17693 100644
--- a/UPGRADE-4.0.md
+++ b/UPGRADE-4.0.md
@@ -1,13 +1,27 @@
 # Upgrade from 3.x to 4.0
 
-There is one change that breaks compatibility with older versions. You'll have to change data type for all your binary resources such as images and fonts from
+There are changes that breaks compatibility with older versions.
 
-```c
-const char MySymbol[] PROGMEM = {
-```
+1. You'll have to change data type for all your binary resources such as images and fonts from
+    
+    ```c
+    const char MySymbol[] PROGMEM = {
+    ```
+    
+    to
+    
+    ```c
+    const uint8_t MySymbol[] PROGMEM = {
+    ```
 
-to
-
-```c
-const uint8_t MySymbol[] PROGMEM = {
-```
+1. Arguments of `setContrast` from `char` to `uint8_t`
+    
+    ```c++
+    void OLEDDisplay::setContrast(char contrast, char precharge, char comdetect);
+    ```
+    
+    to
+    
+    ```c++
+    void OLEDDisplay::setContrast(uint8_t contrast, uint8_t precharge, uint8_t comdetect);
+    ```