diff --git a/configure.ac b/configure.ac
index 7f0c3b98a..bd1260b2a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1752,19 +1752,6 @@ if test "$mercury_cv_int_least64_type" != unknown; then
     AC_DEFINE_UNQUOTED(MR_INT_LEAST64_TYPE, $mercury_cv_int_least64_type)
     MR_INT_LEAST64_TYPE=$mercury_cv_int_least64_type
     AC_SUBST(MR_INT_LEAST64_TYPE)
-
-    if test "$mercury_cv_int_least64_type" = int; then
-        AC_DEFINE_UNQUOTED(MR_INT_LEAST64_LENGTH_MODIFIER, "")
-    elif test "$mercury_cv_int_least64_type" = long; then
-        AC_DEFINE_UNQUOTED(MR_INT_LEAST64_LENGTH_MODIFIER, "l")
-    elif test "$mercury_cv_int_least64_type" = "long long"; then
-        AC_DEFINE_UNQUOTED(MR_INT_LEAST64_LENGTH_MODIFIER, "ll")
-    elif test "$mercury_cv_int_least64_type" = "__int64"; then
-        AC_DEFINE_UNQUOTED(MR_INT_LEAST64_LENGTH_MODIFIER, "I64")
-    else
-        AC_MSG_ERROR(Cannot determine the length modifier for the MR_int_least64_t type.)
-    fi
-    AC_SUBST(MR_INT_LEAST64_LENGTH_MODIFIER)
 fi
 
 #-----------------------------------------------------------------------------#
diff --git a/library/float.m b/library/float.m
index 72dabff96..bd0bd383b 100644
--- a/library/float.m
+++ b/library/float.m
@@ -348,12 +348,9 @@
 :- import_module exception.
 :- import_module int.
 
-%
-% Header files of mathematical significance.
-%
-
 :- pragma foreign_decl("C", "
     #include <float.h>
+    #include <inttypes.h>
     #include <math.h>
 
 #ifdef MR_HAVE_IEEEFP_H
@@ -1166,7 +1163,7 @@ float_to_doc(F) = pretty_printer.float_to_doc(F).
 
 :- pragma foreign_proc("C",
     float32_bits_string(Flt::in) = (Str::uo),
-    [will_not_call_mercury, promise_pure, thread_safe],
+    [will_not_call_mercury, promise_pure, thread_safe, may_not_export_body],
 "
     union {
         float f;
@@ -1181,7 +1178,7 @@ float_to_doc(F) = pretty_printer.float_to_doc(F).
 
 :- pragma foreign_proc("Java",
     float32_bits_string(Flt::in) = (Str::uo),
-    [will_not_call_mercury, promise_pure, thread_safe],
+    [will_not_call_mercury, promise_pure, thread_safe, may_not_export_body],
 "
     float f = (float) Flt;
     int i = Float.floatToIntBits(f);
@@ -1190,7 +1187,7 @@ float_to_doc(F) = pretty_printer.float_to_doc(F).
 
 :- pragma foreign_proc("C#",
     float32_bits_string(Flt::in) = (Str::uo),
-    [will_not_call_mercury, promise_pure, thread_safe],
+    [will_not_call_mercury, promise_pure, thread_safe, may_not_export_body],
 "
     float f = (float) Flt;
     int i = System.BitConverter.ToInt32(System.BitConverter.GetBytes(f), 0);
@@ -1199,7 +1196,7 @@ float_to_doc(F) = pretty_printer.float_to_doc(F).
 
 :- pragma foreign_proc("C",
     float64_bits_string(Flt::in) = (Str::uo),
-    [will_not_call_mercury, promise_pure, thread_safe],
+    [will_not_call_mercury, promise_pure, thread_safe, may_not_export_body],
 "
     #if defined(MR_INT_LEAST64_TYPE)
 
@@ -1210,7 +1207,7 @@ float_to_doc(F) = pretty_printer.float_to_doc(F).
         char buf[64];
 
         u.f = (double) Flt;
-        sprintf(buf, ""%"" MR_INT_LEAST64_LENGTH_MODIFIER ""d"", u.i);
+        sprintf(buf, ""%"" PRIdLEAST64, u.i);
         MR_make_aligned_string_copy(Str, buf);
     #else
         MR_fatal_error(
@@ -1220,7 +1217,7 @@ float_to_doc(F) = pretty_printer.float_to_doc(F).
 
 :- pragma foreign_proc("Java",
     float64_bits_string(Flt::in) = (Str::uo),
-    [will_not_call_mercury, promise_pure, thread_safe],
+    [will_not_call_mercury, promise_pure, thread_safe, may_not_export_body],
 "
     double d = (double) Flt;
     long i = Double.doubleToLongBits(d);
@@ -1229,7 +1226,7 @@ float_to_doc(F) = pretty_printer.float_to_doc(F).
 
 :- pragma foreign_proc("C#",
     float64_bits_string(Flt::in) = (Str::uo),
-    [will_not_call_mercury, promise_pure, thread_safe],
+    [will_not_call_mercury, promise_pure, thread_safe, may_not_export_body],
 "
     double d = (double) Flt;
     long i = System.BitConverter.DoubleToInt64Bits(d);
diff --git a/runtime/mercury_conf.h.in b/runtime/mercury_conf.h.in
index b847ffce1..168f9bcc5 100644
--- a/runtime/mercury_conf.h.in
+++ b/runtime/mercury_conf.h.in
@@ -67,11 +67,6 @@
 
 #undef  MR_INT_LEAST64_TYPE
 
-// MR_INT_LEAST64_LENGTH_MODIFIER: the print() length modifier for
-// a MR_int_least64_t.
-
-#undef  MR_INT_LEAST64_LENGTH_MODIFIER
-
 // MR_INT_LEAST32_TYPE:
 // This must be a C integral type (e.g. short, int, long)
 // without any explicit signedness.
diff --git a/runtime/mercury_types.h b/runtime/mercury_types.h
index 11085e550..85ae23c91 100644
--- a/runtime/mercury_types.h
+++ b/runtime/mercury_types.h
@@ -44,11 +44,13 @@
 #endif
 
 // This section defines types similar to C9X's <stdint.h> header.
-// We do not use <stdint.h>, or the <inttypes.h> or <sys/types.h> files
-// that substitute for it on some systems because (a) some such files
-// do not define the types we need, and (b) some such files include
-// inline function definitions. The latter is a problem because we want to
-// reserve some real machine registers for Mercury abstract machine registers.
+// Historically, we did not use <stdint.h>, or the <inttypes.h> or
+// <sys/types.h> files that substitute for it on some systems because
+// (a) some such files do not define the types we need, and
+// (b) some such files include inline function definitions.
+// While the former reason is very much out of date,
+// the latter may still be a problem because we want to reserve some
+// real machine registers for Mercury abstract machine registers.
 // To be effective, the definitions of these global register variables
 // must precede all function definitions, and we want to put their
 // definitions after mercury_types.h.