diff --git a/src/asm/asmy.y b/src/asm/asmy.y
index 93d3f0f4..e0e89b07 100644
--- a/src/asm/asmy.y
+++ b/src/asm/asmy.y
@@ -1264,19 +1264,38 @@ const		: T_ID					{ $$ = sym_GetConstantValue($1); }
 		| const T_OP_XOR const			{ $$ = $1 ^ $3; }
 		| const T_OP_OR const			{ $$ = $1 | $3; }
 		| const T_OP_AND const			{ $$ = $1 & $3; }
-		| const T_OP_SHL const			{ $$ = $1 << $3; }
-		| const T_OP_SHR const			{ $$ = $1 >> $3; }
+		| const T_OP_SHL const
+		{
+			if ($1 < 0)
+				warning("Left shift of negative value: %d", $1);
+
+			if ($3 < 0)
+				fatalerror("Shift by negative value: %d", $3);
+			else if ($3 >= 32)
+				fatalerror("Shift by too big value: %d", $3);
+
+			$$ = $1 << $3;
+		}
+		| const T_OP_SHR const
+		{
+			if ($3 < 0)
+				fatalerror("Shift by negative value: %d", $3);
+			else if ($3 >= 32)
+				fatalerror("Shift by too big value: %d", $3);
+
+			$$ = $1 >> $3;
+		}
 		| const T_OP_MUL const			{ $$ = $1 * $3; }
 		| const T_OP_DIV const
 		{
 			if ($3 == 0)
-				fatalerror("division by zero");
+				fatalerror("Division by zero");
 			$$ = $1 / $3;
 		}
 		| const T_OP_MOD const
 		{
 			if ($3 == 0)
-				fatalerror("division by zero");
+				fatalerror("Division by zero");
 			$$ = $1 % $3;
 		}
 		| T_OP_ADD const %prec NEG		{ $$ = +$2; }
diff --git a/src/asm/rpn.c b/src/asm/rpn.c
index 7e963d3f..508a563d 100644
--- a/src/asm/rpn.c
+++ b/src/asm/rpn.c
@@ -330,6 +330,15 @@ void rpn_SHL(struct Expression *expr, const struct Expression *src1,
 	     const struct Expression *src2)
 {
 	joinexpr();
+
+	if (src1->nVal < 0)
+		warning("Left shift of negative value: %d", src1->nVal);
+
+	if (src2->nVal < 0)
+		fatalerror("Shift by negative value: %d", src2->nVal);
+	else if (src2->nVal >= 32)
+		fatalerror("Shift by too big value: %d", src2->nVal);
+
 	expr->nVal = (expr->nVal << src2->nVal);
 	pushbyte(expr, RPN_SHL);
 }
@@ -338,6 +347,11 @@ void rpn_SHR(struct Expression *expr, const struct Expression *src1,
 	     const struct Expression *src2)
 {
 	joinexpr();
+	if (src2->nVal < 0)
+		fatalerror("Shift by negative value: %d", src2->nVal);
+	else if (src2->nVal >= 32)
+		fatalerror("Shift by too big value: %d", src2->nVal);
+
 	expr->nVal = (expr->nVal >> src2->nVal);
 	pushbyte(expr, RPN_SHR);
 }
@@ -355,7 +369,7 @@ void rpn_DIV(struct Expression *expr, const struct Expression *src1,
 {
 	joinexpr();
 	if (src2->nVal == 0)
-		fatalerror("division by zero");
+		fatalerror("Division by zero");
 
 	expr->nVal = (expr->nVal / src2->nVal);
 	pushbyte(expr, RPN_DIV);
@@ -366,7 +380,7 @@ void rpn_MOD(struct Expression *expr, const struct Expression *src1,
 {
 	joinexpr();
 	if (src2->nVal == 0)
-		fatalerror("division by zero");
+		fatalerror("Division by zero");
 
 	expr->nVal = (expr->nVal % src2->nVal);
 	pushbyte(expr, RPN_MOD);
diff --git a/test/asm/divzero-instr.out b/test/asm/divzero-instr.out
index 09041a59..e1e0e3e2 100644
--- a/test/asm/divzero-instr.out
+++ b/test/asm/divzero-instr.out
@@ -1,2 +1,2 @@
 ERROR: divzero-instr.asm(2):
-    division by zero
+    Division by zero
diff --git a/test/asm/divzero-section-bank.out b/test/asm/divzero-section-bank.out
index b81d7254..b382e48f 100644
--- a/test/asm/divzero-section-bank.out
+++ b/test/asm/divzero-section-bank.out
@@ -1,2 +1,2 @@
 ERROR: divzero-section-bank.asm(1):
-    division by zero
+    Division by zero