diff --git a/src/scripting/vm/vmexec.h b/src/scripting/vm/vmexec.h
index ec5da180f46..37c0093fa50 100644
--- a/src/scripting/vm/vmexec.h
+++ b/src/scripting/vm/vmexec.h
@@ -899,6 +899,11 @@ static int Exec(VMFrameStack *stack, const VMOP *pc, VMReturn *ret, int numret)
 			ThrowAbortException(X_ARRAY_OUT_OF_BOUNDS, "Max.index = %u, current index = %u\n", BC, reg.d[a]);
 			return 0;
 		}
+		else if (reg.d[a] < 0)
+		{
+			ThrowAbortException(X_ARRAY_OUT_OF_BOUNDS, "Negative current index = %i\n", reg.d[a]);
+			return 0;
+		}
 		NEXTOP;
 
 	OP(BOUND_K):
@@ -908,6 +913,11 @@ static int Exec(VMFrameStack *stack, const VMOP *pc, VMReturn *ret, int numret)
 			ThrowAbortException(X_ARRAY_OUT_OF_BOUNDS, "Max.index = %u, current index = %u\n", konstd[BC], reg.d[a]);
 			return 0;
 		}
+		else if (reg.d[a] < 0)
+		{
+			ThrowAbortException(X_ARRAY_OUT_OF_BOUNDS, "Negative current index = %i\n", reg.d[a]);
+			return 0;
+		}
 		NEXTOP;
 
 	OP(BOUND_R):
@@ -917,6 +927,11 @@ static int Exec(VMFrameStack *stack, const VMOP *pc, VMReturn *ret, int numret)
 			ThrowAbortException(X_ARRAY_OUT_OF_BOUNDS, "Max.index = %u, current index = %u\n", reg.d[B], reg.d[a]);
 			return 0;
 		}
+		else if (reg.d[a] < 0)
+		{
+			ThrowAbortException(X_ARRAY_OUT_OF_BOUNDS, "Negative current index = %i\n", reg.d[a]);
+			return 0;
+		}
 		NEXTOP;
 
 	OP(CONCAT):
diff --git a/src/scripting/vm/vmops.h b/src/scripting/vm/vmops.h
index 97102f5de21..cfdf3fce26c 100644
--- a/src/scripting/vm/vmops.h
+++ b/src/scripting/vm/vmops.h
@@ -122,9 +122,9 @@ xx(THROW,	throw,	THROW,		NOP,	0, 0),		// A == 0: Throw exception object pB
 												// A == 2: (pB == <type of exception thrown>) then pc++ ; next instruction must JMP to another CATCH
 												// A == 3: (pkB == <type of exception thrown>) then pc++ ; next instruction must JMP to another CATCH
 												// for A > 0, exception is stored in pC
-xx(BOUND,	bound,	RII16,		NOP,	0, 0),		// if rA >= BC, throw exception
-xx(BOUND_K,	bound,	LKI,		NOP,	0, 0),		// if rA >= const[BC], throw exception
-xx(BOUND_R,	bound,	RIRI,		NOP,	0, 0),		// if rA >= rB, throw exception
+xx(BOUND,	bound,	RII16,		NOP,	0, 0),		// if rA < 0 or rA >= BC, throw exception
+xx(BOUND_K,	bound,	LKI,		NOP,	0, 0),		// if rA < 0 or rA >= const[BC], throw exception
+xx(BOUND_R,	bound,	RIRI,		NOP,	0, 0),		// if rA < 0 or rA >= rB, throw exception
 
 // String instructions.
 xx(CONCAT,		concat,	RSRSRS,		NOP,	0, 0),		// sA = sB..sC