diff --git a/operand/checks.go b/operand/checks.go
index 2585479d..28de231d 100644
--- a/operand/checks.go
+++ b/operand/checks.go
@@ -35,26 +35,30 @@ func IsIMM2U(op Op) bool {
 
 // IsIMM8 returns true is op is an 8-bit immediate.
 func IsIMM8(op Op) bool {
-	_, ok := op.(U8)
-	return ok
+	_, uok := op.(U8)
+	_, iok := op.(I8)
+	return uok || iok
 }
 
 // IsIMM16 returns true is op is a 16-bit immediate.
 func IsIMM16(op Op) bool {
-	_, ok := op.(U16)
-	return ok
+	_, uok := op.(U16)
+	_, iok := op.(I16)
+	return uok || iok
 }
 
 // IsIMM32 returns true is op is a 32-bit immediate.
 func IsIMM32(op Op) bool {
-	_, ok := op.(U32)
-	return ok
+	_, uok := op.(U32)
+	_, iok := op.(I32)
+	return uok || iok
 }
 
 // IsIMM64 returns true is op is a 64-bit immediate.
 func IsIMM64(op Op) bool {
-	_, ok := op.(U64)
-	return ok
+	_, uok := op.(U64)
+	_, iok := op.(I64)
+	return uok || iok
 }
 
 // IsAL returns true if op is the AL register.
diff --git a/operand/checks_test.go b/operand/checks_test.go
index f6821edd..1d35df5f 100644
--- a/operand/checks_test.go
+++ b/operand/checks_test.go
@@ -36,6 +36,12 @@ func TestChecks(t *testing.T) {
 
 		{IsIMM64, Imm((1 << 64) - 1), true},
 
+		// Signed Immediates
+		{IsIMM8, I8(-1), true},
+		{IsIMM16, I16(-1), true},
+		{IsIMM32, I32(-1), true},
+		{IsIMM64, I64(-1), true},
+
 		// Specific registers
 		{IsAL, reg.AL, true},
 		{IsAL, reg.CL, false},