diff --git a/source/CmdLine.cpp b/source/CmdLine.cpp
index a9d2ba35..073ef21d 100644
--- a/source/CmdLine.cpp
+++ b/source/CmdLine.cpp
@@ -491,6 +491,10 @@ bool ProcessCmdLine(LPSTR lpCmdLine)
 		{
 			RGB_SetInvertBit7(true);
 		}
+		else if (strcmp(lpCmdLine, "-mac-lc-card-dlgr") == 0)	// GH#1258
+		{
+			RGB_SetMacLCCardDLGR(true);
+		}
 		else if (strcmp(lpCmdLine, "-screenshot-and-exit") == 0)	// GH#616: For testing - Use in combination with -load-state
 		{
 			g_cmdLine.szScreenshotFilename = GetCurrArg(lpNextArg);
diff --git a/source/RGBMonitor.cpp b/source/RGBMonitor.cpp
index dc53bf7c..8ce85f7e 100644
--- a/source/RGBMonitor.cpp
+++ b/source/RGBMonitor.cpp
@@ -1049,7 +1049,8 @@ void UpdateDLoResCell (int x, int y, uint16_t addr, bgra_t *pVideoAddress)
 
 	const BYTE auxval_h = auxval >> 4;
 	const BYTE auxval_l = auxval & 0xF;
-	auxval = (ROL_NIB(auxval_h)<<4) | ROL_NIB(auxval_l);
+	if (!RGB_IsMacLCCardDLGR())	// "Apple IIe Card for Macintosh LC" has a bug in its DLGR implementation (GH#1258)
+		auxval = (ROL_NIB(auxval_h)<<4) | ROL_NIB(auxval_l);
 
 	if ((y & 4) == 0)
 	{
@@ -1213,6 +1214,7 @@ static UINT g_rgbFlags = 0;
 static UINT g_rgbMode = 0;
 static WORD g_rgbPrevAN3Addr = 0;
 static bool g_rgbInvertBit7 = false;
+static bool g_rgbMacLCCardDLGR = false;	// TODO: Persist to save-state
 
 // Video7 RGB card:
 // . Clock in the !80COL state to define the 2 flags: F2, F1
@@ -1273,6 +1275,11 @@ bool RGB_IsMixModeInvertBit7(void)
 	return RGB_IsMixMode() && g_rgbInvertBit7;
 }
 
+bool RGB_IsMacLCCardDLGR(void)
+{
+	return g_rgbMacLCCardDLGR;
+}
+
 void RGB_ResetState(void)
 {
 	g_rgbFlags = 0;
@@ -1285,6 +1292,11 @@ void RGB_SetInvertBit7(bool state)
 	g_rgbInvertBit7 = state;
 }
 
+void RGB_SetMacLCCardDLGR(bool state)
+{
+	g_rgbMacLCCardDLGR = state;
+}
+
 //===========================================================================
 
 #define SS_YAML_KEY_RGB_CARD "AppleColor RGB Adaptor"
diff --git a/source/RGBMonitor.h b/source/RGBMonitor.h
index 4b93bf14..0145c85b 100644
--- a/source/RGBMonitor.h
+++ b/source/RGBMonitor.h
@@ -36,8 +36,10 @@ bool RGB_Is160Mode(void);
 bool RGB_IsMixMode(void);
 bool RGB_Is560Mode(void);
 bool RGB_IsMixModeInvertBit7(void);
+bool RGB_IsMacLCCardDLGR(void);
 void RGB_ResetState(void);
 void RGB_SetInvertBit7(bool state);
+void RGB_SetMacLCCardDLGR(bool state);
 
 void RGB_SaveSnapshot(class YamlSaveHelper& yamlSaveHelper);
 void RGB_LoadSnapshot(class YamlLoadHelper& yamlLoadHelper, UINT cardVersion);