diff --git a/src/librustc/middle/infer/mod.rs b/src/librustc/middle/infer/mod.rs
index 6d031c8650756..4e1fffa6ae593 100644
--- a/src/librustc/middle/infer/mod.rs
+++ b/src/librustc/middle/infer/mod.rs
@@ -23,7 +23,7 @@ pub use self::freshen::TypeFreshener;
 
 use middle::subst;
 use middle::subst::Substs;
-use middle::ty::{TyVid, IntVid, FloatVid, RegionVid};
+use middle::ty::{TyVid, IntVid, FloatVid, RegionVid, UnconstrainedNumeric};
 use middle::ty::replace_late_bound_regions;
 use middle::ty::{mod, Ty};
 use middle::ty_fold::{TypeFolder, TypeFoldable};
@@ -519,6 +519,25 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         freshen::TypeFreshener::new(self)
     }
 
+    pub fn type_is_unconstrained_numeric(&'a self, ty: Ty) -> UnconstrainedNumeric {
+        use middle::ty::UnconstrainedNumeric::{Neither, UnconstrainedInt, UnconstrainedFloat};
+        match ty.sty {
+            ty::ty_infer(ty::IntVar(vid)) => {
+                match self.int_unification_table.borrow_mut().get(self.tcx, vid).value {
+                    None => UnconstrainedInt,
+                    _ => Neither,
+                }
+            },
+            ty::ty_infer(ty::FloatVar(vid)) => {
+                match self.float_unification_table.borrow_mut().get(self.tcx, vid).value {
+                    None => return UnconstrainedFloat,
+                    _ => Neither,
+                }
+            },
+            _ => Neither,
+        }
+    }
+
     pub fn combine_fields<'b>(&'b self, a_is_expected: bool, trace: TypeTrace<'tcx>)
                               -> CombineFields<'b, 'tcx> {
         CombineFields {infcx: self,
diff --git a/src/librustc/middle/ty.rs b/src/librustc/middle/ty.rs
index b2cc52ab0a87b..819b39f1eb679 100644
--- a/src/librustc/middle/ty.rs
+++ b/src/librustc/middle/ty.rs
@@ -1495,6 +1495,14 @@ pub enum InferTy {
     FreshIntTy(uint),
 }
 
+#[deriving(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Hash, Show, Copy)]
+pub enum UnconstrainedNumeric {
+    UnconstrainedFloat,
+    UnconstrainedInt,
+    Neither,
+}
+
+
 #[deriving(Clone, RustcEncodable, RustcDecodable, Eq, Hash, Show, Copy)]
 pub enum InferRegion {
     ReVar(RegionVid),
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index fbd40ef6fed0e..9a4dce00f1c30 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -413,7 +413,6 @@ fn check_bare_fn<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
 
             vtable::select_all_fcx_obligations_or_error(&fcx);
             regionck::regionck_fn(&fcx, id, decl, body);
-            fcx.default_diverging_type_variables_to_nil();
             writeback::resolve_type_vars_in_fn(&fcx, decl, body);
         }
         _ => ccx.tcx.sess.impossible_case(body.span,
@@ -1573,10 +1572,24 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
-    pub fn default_diverging_type_variables_to_nil(&self) {
+    /// Apply "fallbacks" to some types
+    /// ! gets replaced with (), unconstrained ints with i32, and unconstrained floats with f64.
+    pub fn default_type_parameters(&self) {
+        use middle::ty::UnconstrainedNumeric::{UnconstrainedInt, UnconstrainedFloat, Neither};
         for (_, &ref ty) in self.inh.node_types.borrow_mut().iter_mut() {
-            if self.infcx().type_var_diverges(self.infcx().resolve_type_vars_if_possible(ty)) {
+            let resolved = self.infcx().resolve_type_vars_if_possible(ty);
+            if self.infcx().type_var_diverges(resolved) {
                 demand::eqtype(self, codemap::DUMMY_SP, *ty, ty::mk_nil(self.tcx()));
+            } else {
+                match self.infcx().type_is_unconstrained_numeric(resolved) {
+                    UnconstrainedInt => {
+                        demand::eqtype(self, codemap::DUMMY_SP, *ty, ty::mk_i32())
+                    },
+                    UnconstrainedFloat => {
+                        demand::eqtype(self, codemap::DUMMY_SP, *ty, ty::mk_f64())
+                    }
+                    Neither => { }
+                }
             }
         }
     }
diff --git a/src/librustc_typeck/check/vtable.rs b/src/librustc_typeck/check/vtable.rs
index e23bf46b564b3..4096908ec312e 100644
--- a/src/librustc_typeck/check/vtable.rs
+++ b/src/librustc_typeck/check/vtable.rs
@@ -279,6 +279,9 @@ pub fn register_object_cast_obligations<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 pub fn select_all_fcx_obligations_or_error(fcx: &FnCtxt) {
     debug!("select_all_fcx_obligations_or_error");
 
+    select_fcx_obligations_where_possible(fcx);
+    fcx.default_type_parameters();
+
     let mut fulfillment_cx = fcx.inh.fulfillment_cx.borrow_mut();
     let r = fulfillment_cx.select_all_or_error(fcx.infcx(),
                                                &fcx.inh.param_env,
diff --git a/src/test/compile-fail/traits-multidispatch-convert-ambig-dest.rs b/src/test/compile-fail/traits-multidispatch-convert-ambig-dest.rs
index 9ceae41d1a465..6ce043ae94b82 100644
--- a/src/test/compile-fail/traits-multidispatch-convert-ambig-dest.rs
+++ b/src/test/compile-fail/traits-multidispatch-convert-ambig-dest.rs
@@ -33,7 +33,7 @@ where T : Convert<U>
 }
 
 fn a() {
-    test(22_i32, 44); //~ ERROR unable to infer
+    test(22_i32, std::default::Default::default()); //~ ERROR unable to infer
 }
 
 fn main() {}
diff --git a/src/test/compile-fail/issue-6458-1.rs b/src/test/run-fail/issue-6458-1.rs
similarity index 92%
rename from src/test/compile-fail/issue-6458-1.rs
rename to src/test/run-fail/issue-6458-1.rs
index 52a57fa2f4411..631517f6a3ca6 100644
--- a/src/test/compile-fail/issue-6458-1.rs
+++ b/src/test/run-fail/issue-6458-1.rs
@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// error-pattern:explicit panic
+
 fn foo<T>(t: T) {}
 fn main() { foo(panic!()) }
-    //~^ ERROR type annotations required
diff --git a/src/test/compile-fail/integer-literal-suffix-inference-2.rs b/src/test/run-pass/integer-literal-suffix-inference-2.rs
similarity index 88%
rename from src/test/compile-fail/integer-literal-suffix-inference-2.rs
rename to src/test/run-pass/integer-literal-suffix-inference-2.rs
index 7c862d04d206d..05973a545a20d 100644
--- a/src/test/compile-fail/integer-literal-suffix-inference-2.rs
+++ b/src/test/run-pass/integer-literal-suffix-inference-2.rs
@@ -11,7 +11,7 @@
 fn foo(_: *const ()) {}
 
 fn main() {
-    let a = 3;  //~ ERROR cannot determine a type for this local variable
+    let a = 3;
     foo(&a as *const _ as *const ());
 }
 
diff --git a/src/test/compile-fail/integer-literal-suffix-inference-3.rs b/src/test/run-pass/integer-literal-suffix-inference-3.rs
similarity index 89%
rename from src/test/compile-fail/integer-literal-suffix-inference-3.rs
rename to src/test/run-pass/integer-literal-suffix-inference-3.rs
index dc3db98566030..05b275a0d8cab 100644
--- a/src/test/compile-fail/integer-literal-suffix-inference-3.rs
+++ b/src/test/run-pass/integer-literal-suffix-inference-3.rs
@@ -10,6 +10,5 @@
 
 fn main() {
     println!("{}", std::mem::size_of_val(&1));
-    //~^ ERROR cannot determine a type for this expression
 }
 
diff --git a/src/test/compile-fail/issue-11382.rs b/src/test/run-pass/issue-11382.rs
similarity index 80%
rename from src/test/compile-fail/issue-11382.rs
rename to src/test/run-pass/issue-11382.rs
index 44f6cd7719d1d..51996614d259f 100644
--- a/src/test/compile-fail/issue-11382.rs
+++ b/src/test/run-pass/issue-11382.rs
@@ -9,8 +9,5 @@
 // except according to those terms.
 
 fn main() {
-panic!(
-    1.2
-//~^ ERROR cannot determine the type of this number; add a suffix to specify the type explicitly
-);
+    println!("{}", 1.2);
 }
diff --git a/src/test/compile-fail/issue-15730.rs b/src/test/run-pass/issue-15730.rs
similarity index 85%
rename from src/test/compile-fail/issue-15730.rs
rename to src/test/run-pass/issue-15730.rs
index c29e74af03cd2..a1a5922e15003 100644
--- a/src/test/compile-fail/issue-15730.rs
+++ b/src/test/run-pass/issue-15730.rs
@@ -12,6 +12,5 @@
 
 fn main() {
     let mut array = [1, 2, 3];
-//~^ ERROR cannot determine a type for this local variable: cannot determine the type of this integ
     let pie_slice = array[1..2];
 }
diff --git a/src/test/compile-fail/issue-16783.rs b/src/test/run-pass/issue-16783.rs
similarity index 84%
rename from src/test/compile-fail/issue-16783.rs
rename to src/test/run-pass/issue-16783.rs
index 1b52bd9c3de9d..cb12d138a5f29 100644
--- a/src/test/compile-fail/issue-16783.rs
+++ b/src/test/run-pass/issue-16783.rs
@@ -10,6 +10,5 @@
 
 pub fn main() {
     let x = [1, 2, 3];
-    //~^ ERROR cannot determine a type for this local variable: cannot determine the type of this
     let y = x.as_slice();
 }
diff --git a/src/test/run-pass/traits-multidispatch-infer-convert-source-and-target.rs b/src/test/run-pass/traits-multidispatch-infer-convert-source-and-target.rs
index c10029791df52..87a5253fd8c6d 100644
--- a/src/test/run-pass/traits-multidispatch-infer-convert-source-and-target.rs
+++ b/src/test/run-pass/traits-multidispatch-infer-convert-source-and-target.rs
@@ -30,6 +30,7 @@ where T : Convert<U>
 }
 
 fn main() {
+    use std::default::Default;
     // T = i16, U = u32
-    test(22, 44,  2, 4);
+    test(Default::default(), Default::default(),  2, 4);
 }
diff --git a/src/test/run-pass/traits-multidispatch-infer-convert-target.rs b/src/test/run-pass/traits-multidispatch-infer-convert-target.rs
index 54515f3b0d7d8..ccf0ce72b4cbb 100644
--- a/src/test/run-pass/traits-multidispatch-infer-convert-target.rs
+++ b/src/test/run-pass/traits-multidispatch-infer-convert-target.rs
@@ -36,11 +36,12 @@ where T : Convert<U>
 }
 
 fn main() {
+    use std::default::Default;
     // T = i16, U = u32
-    test(22_i16, 44,  2, 4);
-    test(22, 44_u32, 2, 4);
+    test(22_i16, Default::default(),  2, 4);
+    test(Default::default(), 44_u32, 2, 4);
 
     // T = u32, U = i16
-    test(22_u32, 44, 4, 2);
-    test(22, 44_i16, 4, 2);
+    test(22_u32, Default::default(), 4, 2);
+    test(Default::default(), 44_i16, 4, 2);
 }