diff --git a/rvgo/fast/vm.go b/rvgo/fast/vm.go
index 3e1755d6..bf9e60bc 100644
--- a/rvgo/fast/vm.go
+++ b/rvgo/fast/vm.go
@@ -587,6 +587,12 @@ func (inst *InstrumentedState) riscvStep() (outErr error) {
 	switch opcode {
 	case 0x03: // 000_0011: memory loading
 		// LB, LH, LW, LD, LBU, LHU, LWU
+
+		// bits[14:12] set to 111 are reserved
+		if eq64(funct3, toU64(0x7)) != 0 {
+			revertWithCode(riscv.ErrInvalidSyscall, fmt.Errorf("illegal instruction %d: reserved instruction encoding", instr))
+		}
+
 		imm := parseImmTypeI(instr)
 		signed := iszero64(and64(funct3, toU64(4)))      // 4 = 100 -> bitflag
 		size := shl64(and64(funct3, toU64(3)), toU64(1)) // 3 = 11 -> 1, 2, 4, 8 bytes size
diff --git a/rvgo/slow/vm.go b/rvgo/slow/vm.go
index 458f00c6..935e1357 100644
--- a/rvgo/slow/vm.go
+++ b/rvgo/slow/vm.go
@@ -760,6 +760,12 @@ func Step(calldata []byte, po PreimageOracle) (stateHash common.Hash, outErr err
 	switch opcode.val() {
 	case 0x03: // 000_0011: memory loading
 		// LB, LH, LW, LD, LBU, LHU, LWU
+
+		// bits[14:12] set to 111 are reserved
+		if eq64(funct3, toU64(0x7)) != (U64{}) {
+			revertWithCode(riscv.ErrInvalidSyscall, fmt.Errorf("illegal instruction %d: reserved instruction encoding", instr))
+		}
+
 		imm := parseImmTypeI(instr)
 		signed := iszero64(and64(funct3, toU64(4)))      // 4 = 100 -> bitflag
 		size := shl64(and64(funct3, toU64(3)), toU64(1)) // 3 = 11 -> 1, 2, 4, 8 bytes size
diff --git a/rvsol/src/RISCV.sol b/rvsol/src/RISCV.sol
index 1bbb681e..a5c76090 100644
--- a/rvsol/src/RISCV.sol
+++ b/rvsol/src/RISCV.sol
@@ -1147,6 +1147,10 @@ contract RISCV is IBigStepper {
                 let pc_ := _pc
                 // 000_0011: memory loading
                 // LB, LH, LW, LD, LBU, LHU, LWU
+
+                // bits[14:12] set to 111 are reserved
+                if eq64(funct3, toU64(0x7)) { revertWithCode(0xf001ca11) }
+
                 let imm := parseImmTypeI(instr)
                 let signed := iszero64(and64(funct3, toU64(4))) // 4 = 100 -> bitflag
                 let size := shl64(and64(funct3, toU64(3)), toU64(1)) // 3 = 11 -> 1, 2, 4, 8 bytes size