[geeks] Odd SVR3.2 f77 problem

[The Pitlog]

I'm playing with the fortran (f77) compiler on an AT&T 3b2/600 running
SVR3.2.3 and have a problem. This program:
                program test
                read(5,10) x
10              format(f4.1)
                stop
                end

compiles fine but throws an error every time:

$ ./x
2.3
Illegal instruction - core dumped
$

I've tried everything I know of to fix, though admittedly my f77 skilz are
highly rusty. The same program works fine when using an integer variable and
integer format statement.

I'm linking with libF77.a and can't see another library that I might be
missing. The machine does have floating point capabilities as far as I know.

Any ideas?