diff --git a/Machines/PCCompatible/CGA.hpp b/Machines/PCCompatible/CGA.hpp
index 547cb24cd..897924656 100644
--- a/Machines/PCCompatible/CGA.hpp
+++ b/Machines/PCCompatible/CGA.hpp
@@ -263,7 +263,9 @@ class CGA {
 				// character code + attributes except that these are two bytes worth of graphics.
 				//
 				// Meanwhile, row address is used to invent a 15th address line.
-				const auto base_address = ((state.refresh_address << 1) + (state.row_address << 13)) & 0x3fff;
+				const auto base_address =
+					((state.refresh_address & 0xfff) << 1) +
+					((state.row_address & 1) << 13);
 				const uint8_t bitmap[] = {
 					ram[base_address],
 					ram[base_address + 1],
@@ -299,8 +301,8 @@ class CGA {
 			}
 
 			void serialise_text(const Motorola::CRTC::BusState &state) {
-				const uint8_t attributes = ram[((state.refresh_address << 1) + 1) & 0xfff];
-				const uint8_t glyph = ram[((state.refresh_address << 1) + 0) & 0xfff];
+				const uint8_t attributes = ram[((state.refresh_address << 1) + 1) & 0x3fff];
+				const uint8_t glyph = ram[((state.refresh_address << 1) + 0) & 0x3fff];
 				const uint8_t row = font[(glyph * 8) + state.row_address];
 
 				uint8_t colours[2] = {