diff --git a/FlippR-Driver/include/output/IEightDigitDisplay.h b/FlippR-Driver/include/output/IEightDigitDisplay.h
index 4346f6c..8f3806d 100644
--- a/FlippR-Driver/include/output/IEightDigitDisplay.h
+++ b/FlippR-Driver/include/output/IEightDigitDisplay.h
@@ -5,6 +5,8 @@
 #ifndef FLIPPR_DRIVER_IEIGHTDIGITDISPLAY_H
 #define FLIPPR_DRIVER_IEIGHTDIGITDISPLAY_H
 
+#include "IOutputDisplay.h"
+
 #include <array>
 
 namespace flippr_driver
@@ -12,11 +14,10 @@ namespace flippr_driver
 namespace output
 {
 
-class IEightDigitDisplay
+class IEightDigitDisplay : public IOutputDisplay
 {
 public:
-  virtual void write_score(int score);
-  virtual void write_content(std::array<char, 8> content);
+  virtual void write_content(std::array<char, 8> content) = 0;
 };
 
 }
diff --git a/FlippR-Driver/include/output/IOutputDisplay.h b/FlippR-Driver/include/output/IOutputDisplay.h
index bddd0b0..59f414e 100644
--- a/FlippR-Driver/include/output/IOutputDisplay.h
+++ b/FlippR-Driver/include/output/IOutputDisplay.h
@@ -21,7 +21,6 @@ public:
   virtual ~IDisplay();
 
   virtual void write_score(int score) = 0;
-  virtual void write_content(std::array<char, DigitCount> content) = 0;
 };
 
 }
diff --git a/FlippR-Driver/include/output/ISevenDigitDisplay.h b/FlippR-Driver/include/output/ISevenDigitDisplay.h
index 7d85392..b51cc81 100644
--- a/FlippR-Driver/include/output/ISevenDigitDisplay.h
+++ b/FlippR-Driver/include/output/ISevenDigitDisplay.h
@@ -5,6 +5,8 @@
 #ifndef FLIPPR_DRIVER_ISEVENDIGITDISPLAY_H
 #define FLIPPR_DRIVER_ISEVENDIGITDISPLAY_H
 
+#include "IOutputDisplay.h"
+
 #include <array>
 
 namespace flippr_driver
@@ -12,11 +14,10 @@ namespace flippr_driver
 namespace output
 {
 
-class ISevenDigitDisplay
+class ISevenDigitDisplay : public IOutputDisplay
 {
 public:
-  virtual void write_score(int score);
-  virtual void write_content(std::array<char, 7> content);
+  virtual void write_content(std::array<char, 7> content) = 0;
 };
 
 }