diff --git a/src/asm/asmy.y b/src/asm/asmy.y
index 1ea0a672..6264f74e 100644
--- a/src/asm/asmy.y
+++ b/src/asm/asmy.y
@@ -142,8 +142,9 @@ void	copyrept( void )
 {
 	SLONG	level=1, len, instring=0;
 	char	*src=pCurrentBuffer->pBuffer;
+	char	*bufferEnd = pCurrentBuffer->pBufferStart + pCurrentBuffer->nBufferSize;
 
-	while( *src && level )
+	while( src < bufferEnd && level )
 	{
 		if( instring==0 )
 		{
@@ -221,8 +222,9 @@ void	copymacro( void )
 {
 	SLONG	level=1, len, instring=0;
 	char	*src=pCurrentBuffer->pBuffer;
+	char	*bufferEnd = pCurrentBuffer->pBufferStart + pCurrentBuffer->nBufferSize;
 
-	while( *src && level )
+	while( src < bufferEnd && level )
 	{
 		if( instring==0 )
 		{
diff --git a/src/asm/rpn.c b/src/asm/rpn.c
index 3a8dba27..2bc9d94c 100644
--- a/src/asm/rpn.c
+++ b/src/asm/rpn.c
@@ -316,6 +316,9 @@ rpn_DIV(struct Expression * expr, struct Expression * src1,
     struct Expression * src2)
 {
 	joinexpr();
+	if (src2->nVal == 0) {
+		fatalerror("division by zero");
+	}
 	expr->nVal = (expr->nVal / src2->nVal);
 	pushbyte(expr, RPN_DIV);
 }
@@ -325,6 +328,9 @@ rpn_MOD(struct Expression * expr, struct Expression * src1,
     struct Expression * src2)
 {
 	joinexpr();
+	if (src2->nVal == 0) {
+		fatalerror("division by zero");
+	}
 	expr->nVal = (expr->nVal % src2->nVal);
 	pushbyte(expr, RPN_MOD);
 }