diff --git a/src/emucore/Cart2K.hxx b/src/emucore/Cart2K.hxx
index 13aed2608..ddca38048 100644
--- a/src/emucore/Cart2K.hxx
+++ b/src/emucore/Cart2K.hxx
@@ -118,6 +118,13 @@ class Cartridge2K : public Cartridge
     }
   #endif
 
+    /**
+      Get the byte at the specified address.
+
+      @return The byte at the specified address
+    */
+    uInt8 peek(uInt16 address) override { return myImage[address & myMask]; }
+
   private:
     // Pointer to a dynamically allocated ROM image of the cartridge
     BytePtr myImage;
diff --git a/src/emucore/Cart4K.hxx b/src/emucore/Cart4K.hxx
index cc361feba..f8ad3c6fa 100644
--- a/src/emucore/Cart4K.hxx
+++ b/src/emucore/Cart4K.hxx
@@ -115,6 +115,13 @@ class Cartridge4K : public Cartridge
     }
   #endif
 
+    /**
+      Get the byte at the specified address.
+
+      @return The byte at the specified address
+    */
+    uInt8 peek(uInt16 address) override { return myImage[address & 0x0FFF]; }
+
   private:
     // The 4K ROM image for the cartridge
     uInt8 myImage[4096];
diff --git a/src/emucore/Device.hxx b/src/emucore/Device.hxx
index 73dd90f93..7ab55597e 100644
--- a/src/emucore/Device.hxx
+++ b/src/emucore/Device.hxx
@@ -85,7 +85,7 @@ class Device : public Serializable
 
       @return The byte at the specified address
     */
-    virtual uInt8 peek(uInt16 address) { return 0; }
+    virtual uInt8 peek(uInt16 address) = 0;
 
     /**
       Change the byte at the specified address to the given value