diff --git a/clock/clock.c b/clock/clock.c
index f79736f..a987490 100644
--- a/clock/clock.c
+++ b/clock/clock.c
@@ -31,7 +31,8 @@ volatile struct timeval_t time = {
     .seconds = 0,
     .minutes = 0,
     .hours = 0,
-    .milliseconds = 0
+    .milliseconds = 0,
+    .dirty = 0
 };
 
 #ifdef STOP_WATCH
@@ -93,6 +94,8 @@ void increaseTime() {
     if(time.hours == 24) {
         time.hours = 0;
     }
+
+    time.dirty = 1;
 }
 
 void descreaseTime() {
@@ -122,6 +125,8 @@ void descreaseTime() {
     if(time.hours == 255) {
         time.hours = 23;
     }
+
+    time.dirty = 1;
 }
 
 void resetTime() {
@@ -129,6 +134,7 @@ void resetTime() {
     time.hours = 0;
     time.minutes = 0;
     time.seconds = 0;
+    time.dirty = 1;
 }
 
 void switchToNextMode() {
@@ -167,19 +173,24 @@ inline uint8_t getMode() {
 }
 
 void printTime(bitmap_t destination, const enum CLOCK_THEME theme) {
-    switch(theme) {
-        case THEME_ANALOG:
-            pt_analogClock(destination, time, currentMode);
-            break;
-        case THEME_BARS:
-            pt_raisingBars(destination, time, currentMode);
-            break;
-        case THEME_BINARY:
-            pt_simpleBinary(destination, time, currentMode);
-            break;
-        case THEME_DICES:
-            pt_dices(destination, time, currentMode);
-            break;
+    if(time.dirty)
+    {
+        switch(theme) {
+            case THEME_ANALOG:
+                pt_analogClock(destination, time, currentMode);
+                break;
+            case THEME_BARS:
+                pt_raisingBars(destination, time, currentMode);
+                break;
+            case THEME_BINARY:
+                pt_simpleBinary(destination, time, currentMode);
+                break;
+            case THEME_DICES:
+                pt_dices(destination, time, currentMode);
+                break;
+        }
+
+        time.dirty = 0;
     }
 }
 
diff --git a/clock/clock.h b/clock/clock.h
index 8f1ca23..ea97337 100644
--- a/clock/clock.h
+++ b/clock/clock.h
@@ -45,6 +45,7 @@ enum CLOCK_THEME {
 struct timeval_t {
     uint8_t seconds, minutes, hours;
     uint16_t milliseconds;
+    uint8_t dirty;
 };
 
 /**
diff --git a/main.c b/main.c
index b1e71d7..a7bc22f 100644
--- a/main.c
+++ b/main.c
@@ -34,7 +34,6 @@ int main(void)
     while(1) {
         handleKeyInput();
 
-        // XXX: this should only be called if there is actually something new
         printTime(bitmap, THEME_BARS);
         scanout(bitmap);
     }