[plt-scheme] If expressions in Embedded PLT Scheme

I am embedding MzScheme/PLT Scheme in a program.

In MzScheme (v372 is the one I had been using), it was permissible to  
write if expressions without an alternate, as in

   (if (> x 1) (display x))

When I embed the new PLT Scheme (v401, I think), for the same  
expression, I get an error message that it 'must have an "else"  
expression'.

R6RS seems to suggest that the no-alternate form is still valid

   http://www.r6rs.org/final/html/r6rs/r6rs-Z-H-14.html#node_sec_11.4.3

Is there a way to turn off the "require alternate" behavior in  
embedded PLT Scheme?

Thanks!

-- Sam Rebelsky