diff --git a/internal/commands/for.go b/internal/commands/for.go
index 5bb681c..79a8bcb 100644
--- a/internal/commands/for.go
+++ b/internal/commands/for.go
@@ -2,6 +2,7 @@ package commands
 
 import (
 	"fmt"
+	"os"
 	"strings"
 
 	"c65gm/internal/compiler"
@@ -106,6 +107,26 @@ func (c *ForCommand) Interpret(line preproc.Line, ctx *compiler.CompilerContext)
 		IsVar:   endIsVar,
 	}
 
+	if c.varKind == compiler.KindByte {
+		// Error on literal out of range
+		if !c.startOp.IsVar && c.startOp.Value > 255 {
+			return fmt.Errorf("FOR: BYTE variable cannot start at literal %d (max 255)", c.startOp.Value)
+		}
+		if !c.endOp.IsVar && c.endOp.Value > 255 {
+			return fmt.Errorf("FOR: BYTE variable cannot loop to literal %d (max 255)", c.endOp.Value)
+		}
+
+		// Warn on variable type mismatch
+		if c.startOp.IsVar && c.startOp.VarKind == compiler.KindWord {
+			_, _ = fmt.Fprintf(os.Stderr, "%s:%d: warning: BYTE loop variable with WORD start value truncates to low byte\n",
+				line.Filename, line.LineNo)
+		}
+		if c.endOp.IsVar && c.endOp.VarKind == compiler.KindWord {
+			_, _ = fmt.Fprintf(os.Stderr, "%s:%d: warning: BYTE loop variable with WORD end value may cause infinite loop\n",
+				line.Filename, line.LineNo)
+		}
+	}
+
 	// Parse optional STEP
 	if len(params) == 8 {
 		if strings.ToUpper(params[6]) != "STEP" {