diff --git a/src/gbasm/errors.c b/src/gbasm/errors.c
index c7f9533..fc30e7c 100644
--- a/src/gbasm/errors.c
+++ b/src/gbasm/errors.c
@@ -54,3 +54,13 @@ void gbasm_too_few_args_error(const struct gbasm_parsed_inst *inst,
 
 	exit(1);
 }
+
+void gbasm_invalid_imm_error(const struct gbasm_parsed_inst *inst,
+                             const struct gbasm_op_info *opcode)
+{
+	gbasm_print_error(
+		"ERROR: %s:%d out of bounds constant for opcode \"%s\"\n",
+		inst->file_name, inst->line_num, inst->opcode);
+
+	exit(1);
+}
diff --git a/src/gbasm/errors.h b/src/gbasm/errors.h
index b1edc8d..6f2fa4b 100644
--- a/src/gbasm/errors.h
+++ b/src/gbasm/errors.h
@@ -14,4 +14,6 @@ void gbasm_arg_wrong_type_error(const struct gbasm_parsed_inst *inst,
 void gbasm_too_few_args_error(const struct gbasm_parsed_inst *inst,
                               const struct gbasm_op_info *opcode);
 
+void gbasm_invalid_imm_error(const struct gbasm_parsed_inst *inst,
+                             const struct gbasm_op_info *opcode);
 #endif
diff --git a/src/gbasm/gb_types.h b/src/gbasm/gb_types.h
index 5949042..86ee38e 100644
--- a/src/gbasm/gb_types.h
+++ b/src/gbasm/gb_types.h
@@ -43,7 +43,7 @@ struct gbasm_operand_r16 {
 };
 
 struct gbasm_operand_imm {
-	uint16_t value;
+	int value;
 };
 
 enum gbasm_operand_cond_type {
diff --git a/src/gbasm/opcodes.c b/src/gbasm/opcodes.c
index 68dba8b..eb8ccf9 100644
--- a/src/gbasm/opcodes.c
+++ b/src/gbasm/opcodes.c
@@ -15,9 +15,10 @@ static bool gbasm_argtype_in_set(uint32_t argtype_set, uint32_t argtype)
 	return !!(argtype & argtype_set);
 }
 
-static bool imm_is_8_bit(uint16_t val)
+static bool imm_is_8_bit(int val)
 {
-	return (val <= 127) && (val >= -128);
+	/* Allow signed or unsigned representation */
+	return (val <= 255) && (val >= -128);
 }
 
 static int check_no_args(const struct gbasm_parsed_inst *inst,
@@ -94,9 +95,13 @@ static int ld_check(const struct gbasm_parsed_inst *inst,
 		gbasm_arg_wrong_type_error(inst, op_info);
 	}
 
-	if (inst->operands[0].type == GBASM_OPERAND_REG_8 &&
-	    imm_is_8_bit(inst->operands[1].imm.value)) {
+	if (inst->operands[0].type == GBASM_OPERAND_REG_8) {
+		if (!imm_is_8_bit(inst->operands[1].imm.value)) {
+			DEBUG_LOG("inst->operands[1].imm.value = %d",
+			          inst->operands[1].imm.value);
 
+			gbasm_invalid_imm_error(inst, op_info);
+		}
 	}
 
 	return 0;
diff --git a/src/gbasm/tests/ld.c b/src/gbasm/tests/ld.c
index c53d76d..2a0545e 100644
--- a/src/gbasm/tests/ld.c
+++ b/src/gbasm/tests/ld.c
@@ -3,22 +3,40 @@
 
 #include <string.h>
 
-void init_r8(void);
+void init_r8_r8(void);
+void init_r8_d8(void);
 
-static char ld_r8_src[1024] = { 0 };
+/*
+ * Data for LD R8, R8 tests
+ */
+static char ld_r8_r8_src[1024] = { 0 };
+static uint8_t ld_r8_r8_output[0x40];
 
-static uint8_t ld_r8_output[0x40];
+struct gbasm_test r8_r8 = {
+	.init = init_r8_r8,
+	.name = "r8/r8",
+	.asm_source = ld_r8_r8_src,
+	.expected_output = ld_r8_r8_output,
+	.expected_output_len = 0,
+};
 
-struct gbasm_test r8 = {
-	.init = init_r8,
-	.name = "r8",
-	.asm_source = ld_r8_src,
-	.expected_output = ld_r8_output,
+/*
+ * Data for LD R8, D8 tests
+ */
+static char ld_r8_d8_src[1024] = { 0 };
+static uint8_t ld_r8_d8_output[0x40];
+
+struct gbasm_test r8_d8 = {
+	.init = init_r8_d8,
+	.name = "r8/d8",
+	.asm_source = ld_r8_d8_src,
+	.expected_output = ld_r8_d8_output,
 	.expected_output_len = 0,
 };
 
 static const struct gbasm_test *tests[] = {
-	&r8,
+	&r8_r8,
+	&r8_d8,
 };
 
 struct gbasm_tests gbasm_ld_tests = {
@@ -38,7 +56,7 @@ const char *operands[] = {
 	"A",
 };
 
-void gen_r8_src(void)
+void gen_r8_r8_src(void)
 {
 	const char *src, *dst;
 	size_t len = 0;
@@ -55,16 +73,16 @@ void gen_r8_src(void)
 				continue;
 			}
 
-			len += sprintf(ld_r8_src + len, "ld %s %s\n", src, dst);
+			len += sprintf(ld_r8_r8_src + len, "ld %s %s\n", src, dst);
 		}
 	}
 
-	sprintf(ld_r8_src + len, "halt");
+	sprintf(ld_r8_r8_src + len, "halt");
 
-	DEBUG_LOG("%s", ld_r8_src);
+	DEBUG_LOG("%s", ld_r8_r8_src);
 }
 
-void gen_r8_output(void)
+void gen_r8_r8_output(void)
 {
 	int num_insts = ARRAY_SIZE(operands) * ARRAY_SIZE(operands);
 	int halt_code = 0x76;
@@ -75,15 +93,38 @@ void gen_r8_output(void)
 			continue;
 		}
 
-		ld_r8_output[i++] = opcode;
+		ld_r8_r8_output[i++] = opcode;
 	}
 
-	ld_r8_output[i] = halt_code;
-	r8.expected_output_len = num_insts;
+	ld_r8_r8_output[i] = halt_code;
+	r8_r8.expected_output_len = num_insts;
 }
 
-void init_r8(void)
+void init_r8_r8(void)
 {
-	gen_r8_src();
-	gen_r8_output();
+	gen_r8_r8_src();
+	gen_r8_r8_output();
+}
+
+void gen_r8_d8_src(void)
+{
+	snprintf(ld_r8_d8_src,
+	         sizeof(ld_r8_d8_src),
+	         "ld a, $12\n"
+	         "ld b, $0\n"
+	         "ld c, $0xff\n"
+	         "ld d, $127\n"
+	         "ld e, $0xfe\n"
+	         "ld h, $-1\n"
+	         "ld l, $-128");
+}
+
+void gen_r8_d8_output(void)
+{
+}
+
+void init_r8_d8(void)
+{
+	gen_r8_d8_src();
+	gen_r8_d8_output();
 }