diff --git a/src/Makefile b/src/Makefile
index bd084e0246e82..ccf7bb21508d6 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -419,7 +419,8 @@ self: $(CFG_RUSTC)
 
 # Float doesn't work in boot
 
-FLOAT_XFAILS := test/run-pass/float.rs
+FLOAT_XFAILS := test/run-pass/float.rs \
+                test/run-pass/float2.rs
 
 # Temporarily xfail tests broken by the nominal-tags change.
 
diff --git a/src/comp/front/ast.rs b/src/comp/front/ast.rs
index cdeea2418098a..d48792d117ea6 100644
--- a/src/comp/front/ast.rs
+++ b/src/comp/front/ast.rs
@@ -256,6 +256,7 @@ tag lit_ {
     lit_uint(uint);
     lit_mach_int(ty_mach, int);
     lit_float(str);
+    lit_mach_float(ty_mach, str);
     lit_nil;
     lit_bool(bool);
 }
diff --git a/src/comp/front/lexer.rs b/src/comp/front/lexer.rs
index d4948503d5964..b2c681b1754bf 100644
--- a/src/comp/front/lexer.rs
+++ b/src/comp/front/lexer.rs
@@ -3,6 +3,9 @@ import std._str;
 import std._int;
 import std.map;
 import std.map.hashmap;
+import std.option;
+import std.option.some;
+import std.option.none;
 import util.common;
 import util.common.new_str_hash;
 
@@ -333,6 +336,28 @@ impure fn scan_dec_digits(reader rdr) -> int {
     ret accum_int;
 }
 
+impure fn scan_exponent(reader rdr) -> option.t[int] {
+    auto c = rdr.curr();
+    auto sign = 1;
+
+    if(c == 'e' || c == 'E') {
+        rdr.bump();
+        c = rdr.curr();
+        if(c == '-') {
+            sign = -1;
+            rdr.bump();
+        }
+        else if(c == '+') {
+            rdr.bump();
+        }
+        auto exponent = scan_dec_digits(rdr);
+        ret(some(sign * exponent));
+    }
+    else {
+        ret none[int];
+    }
+}
+
 impure fn scan_number(mutable char c, reader rdr) -> token.token {
     auto accum_int = 0;
     auto n = rdr.next();
@@ -364,7 +389,7 @@ impure fn scan_number(mutable char c, reader rdr) -> token.token {
     } else {
         accum_int = scan_dec_digits(rdr);
     }
-
+        
     c = rdr.curr();
     n = rdr.next();
 
@@ -418,17 +443,54 @@ impure fn scan_number(mutable char c, reader rdr) -> token.token {
             ret token.LIT_UINT(accum_int as uint);
         }
     }
-    n = rdr.curr();
-    if(n == '.') {
+    c = rdr.curr();
+    if(c == '.') {
         // Parse a floating-point number.
         rdr.bump();
         auto accum_int1 = scan_dec_digits(rdr);
-        ret token.LIT_FLOAT(_int.to_str(accum_int, 10u) + "."
-                          + _int.to_str(accum_int1, 10u));
-        // FIXME: Parse exponent.
+        auto base_str =   _int.to_str(accum_int, 10u) + "."
+            + _int.to_str(accum_int1, 10u);
+        c = rdr.curr();
+        auto exponent_str = "";
+        let option.t[int] maybe_exponent = scan_exponent(rdr);
+        alt(maybe_exponent) {
+            case(some[int](?i)) {
+                exponent_str = "e" + _int.to_str(i, 10u);
+            }
+            case(none[int]) {
+            }
+        }
+
+        c = rdr.curr();
+        if(c == 'f') {
+            rdr.bump();
+            c = rdr.curr();
+            n = rdr.next();
+            if(c == '3' && n == '2') {
+                rdr.bump(); rdr.bump();
+                ret token.LIT_MACH_FLOAT(util.common.ty_f32,
+                                         base_str + exponent_str);
+            }
+            else if(c == '6' && n == '4') {
+                rdr.bump(); rdr.bump();
+                ret token.LIT_MACH_FLOAT(util.common.ty_f64,
+                                         base_str + exponent_str);
+            }
+        }
+        else {
+            ret token.LIT_FLOAT(base_str + exponent_str);
+        }
     }
-    else {
-        ret token.LIT_INT(accum_int);
+
+    auto maybe_exponent = scan_exponent(rdr);
+    alt(maybe_exponent) {
+        case(some[int](?i)) {
+            ret token.LIT_FLOAT(_int.to_str(accum_int, 10u)
+                                + "e" + _int.to_str(i, 10u));
+        }
+        case(none[int]) {                   
+            ret token.LIT_INT(accum_int);
+        }
     }
 }
 
diff --git a/src/comp/front/parser.rs b/src/comp/front/parser.rs
index f1f8a91887f14..9e13e706af4eb 100644
--- a/src/comp/front/parser.rs
+++ b/src/comp/front/parser.rs
@@ -545,6 +545,10 @@ impure fn parse_lit(parser p) -> ast.lit {
             p.bump();
             lit = ast.lit_mach_int(tm, i);
         }
+        case (token.LIT_MACH_FLOAT(?tm, ?s)) {
+            p.bump();
+            lit = ast.lit_mach_float(tm, s);
+        }
         case (token.LIT_CHAR(?c)) {
             p.bump();
             lit = ast.lit_char(c);
diff --git a/src/comp/front/token.rs b/src/comp/front/token.rs
index a1fb1cd0174f7..46fd0735641f2 100644
--- a/src/comp/front/token.rs
+++ b/src/comp/front/token.rs
@@ -127,6 +127,7 @@ tag token {
     LIT_UINT(uint);
     LIT_MACH_INT(ty_mach, int);
     LIT_FLOAT(str);
+    LIT_MACH_FLOAT(ty_mach, str);
     LIT_STR(str);
     LIT_CHAR(char);
     LIT_BOOL(bool);
diff --git a/src/comp/middle/trans.rs b/src/comp/middle/trans.rs
index b75af85038686..ebae4844da174 100644
--- a/src/comp/middle/trans.rs
+++ b/src/comp/middle/trans.rs
@@ -763,6 +763,10 @@ fn C_float(str s) -> ValueRef {
     ret llvm.LLVMConstRealOfString(T_float(), _str.buf(s));
 }
 
+fn C_floating(str s, TypeRef t) -> ValueRef {
+    ret llvm.LLVMConstRealOfString(t, _str.buf(s));
+}
+
 fn C_nil() -> ValueRef {
     // NB: See comment above in T_void().
     ret C_integral(0, T_i1());
@@ -2338,6 +2342,14 @@ fn trans_lit(@crate_ctxt cx, &ast.lit lit, &ast.ann ann) -> ValueRef {
         case(ast.lit_float(?fs)) {
             ret C_float(fs);
         }
+        case(ast.lit_mach_float(?tm, ?s)) {
+            auto t = T_float();
+            alt(tm) {
+                case(common.ty_f32) { t = T_f32(); }
+                case(common.ty_f64) { t = T_f64(); }
+            }
+            ret C_floating(s, t);
+        }
         case (ast.lit_char(?c)) {
             ret C_integral(c as int, T_char());
         }
@@ -4582,13 +4594,34 @@ fn trans_log(@block_ctxt cx, @ast.expr e) -> result {
 
     auto sub = trans_expr(cx, e);
     auto e_ty = ty.expr_ty(e);
-    alt (e_ty.struct) {
-        case(ty.ty_float) {
-            auto tmp = sub.bcx.build.Alloca(T_float());
+    if(ty.type_is_fp(e_ty)) {
+        let TypeRef tr;
+        let bool is32bit = false;
+        alt(e_ty.struct) {
+            case(ty.ty_machine(util.common.ty_f32)) {
+                tr = T_f32();
+                is32bit = true;
+            }
+            case(ty.ty_machine(util.common.ty_f64)) {
+                tr = T_f64();
+            }
+            case(_) {
+                tr = T_float();
+            }
+        }
+        if(is32bit) {
+            ret trans_upcall(sub.bcx,
+                             "upcall_log_float",
+                             vec(sub.val));
+        }
+        else {
+            auto tmp = sub.bcx.build.Alloca(tr);
             sub.bcx.build.Store(sub.val, tmp);
-            sub = res(sub.bcx, tmp);
+            auto v = vp2i(sub.bcx, tmp);
+            ret trans_upcall(sub.bcx,
+                             "upcall_log_double",
+                             vec(v));
         }
-        case(_) { }
     }
 
     alt (e_ty.struct) {
@@ -4598,12 +4631,6 @@ fn trans_log(@block_ctxt cx, @ast.expr e) -> result {
                              "upcall_log_str",
                              vec(v));
         }
-        case (ty.ty_float) {
-            auto v = vp2i(sub.bcx, sub.val);
-            ret trans_upcall(sub.bcx,
-                             "upcall_log_float",
-                             vec(v));
-        }
         case (_) {
             ret trans_upcall(sub.bcx,
                              "upcall_log_int",
diff --git a/src/comp/middle/typeck.rs b/src/comp/middle/typeck.rs
index dbeeb8f903e50..6767d59d8bb29 100644
--- a/src/comp/middle/typeck.rs
+++ b/src/comp/middle/typeck.rs
@@ -1497,7 +1497,8 @@ fn check_lit(@ast.lit lit) -> @ty.t {
         case (ast.lit_str(_))           { sty = ty.ty_str;  }
         case (ast.lit_char(_))          { sty = ty.ty_char; }
         case (ast.lit_int(_))           { sty = ty.ty_int;  }
-        case (ast.lit_float(_))           { sty = ty.ty_float;  }
+        case (ast.lit_float(_))         { sty = ty.ty_float;  }
+        case (ast.lit_mach_float(?tm, _)) { sty = ty.ty_machine(tm); }
         case (ast.lit_uint(_))          { sty = ty.ty_uint; }
         case (ast.lit_mach_int(?tm, _)) { sty = ty.ty_machine(tm); }
         case (ast.lit_nil)              { sty = ty.ty_nil;  }
diff --git a/src/rt/rust_upcall.cpp b/src/rt/rust_upcall.cpp
index 30306104859c6..19f1ec9070d08 100644
--- a/src/rt/rust_upcall.cpp
+++ b/src/rt/rust_upcall.cpp
@@ -40,7 +40,14 @@ void upcall_log_int(rust_task *task, int32_t i) {
 }
 
 extern "C" CDECL
-void upcall_log_float(rust_task *task, double *f) {
+void upcall_log_float(rust_task *task, float f) {
+    LOG_UPCALL_ENTRY(task);
+    task->log(rust_log::UPCALL | rust_log::ULOG,
+              "rust: %12.12f", f);
+}
+
+extern "C" CDECL
+void upcall_log_double(rust_task *task, double *f) {
     LOG_UPCALL_ENTRY(task);
     task->log(rust_log::UPCALL | rust_log::ULOG,
               "rust: %12.12f", *f);
diff --git a/src/test/run-pass/float2.rs b/src/test/run-pass/float2.rs
new file mode 100644
index 0000000000000..0c111ba9779e8
--- /dev/null
+++ b/src/test/run-pass/float2.rs
@@ -0,0 +1,23 @@
+fn main() {
+  auto a = 1.5e6;
+  auto b = 1.5E6;
+  auto c = 1e6;
+  auto d = 1E6;
+  auto e = 3.0f32;
+  auto f = 5.9f64;
+  auto g = 1.e6f32;
+  auto h = 1.0e7f64;
+  auto i = 1.0E7f64;
+  auto j = 3.1e+9;
+  auto k = 3.2e-10;
+ 
+  check(a == b);
+  check(c < b);
+  check(c == d);
+  check(e < g);
+  check(f < h);
+  check(g == 1000000.0f32);
+  check(h == i);
+  check(j > k);
+  check(k < a);
+}
\ No newline at end of file