diff --git a/base/inference.jl b/base/inference.jl
index 026f5c43a3f08..f76dfb1e973ae 100644
--- a/base/inference.jl
+++ b/base/inference.jl
@@ -63,6 +63,11 @@ immutable Const
     Const(v::ANY) = new(v)
 end
 
+function rewrap(t::ANY, u::ANY)
+    isa(t, Const) && return t
+    rewrap_unionall(t, u)
+end
+
 type InferenceState
     sp::SimpleVector     # static parameters
     label_counter::Int   # index of the current highest label for this function
@@ -149,9 +154,9 @@ type InferenceState
                     end
                     s_types[1][la] = VarState(Tuple, false)
                 else
-                    s_types[1][la] = VarState(rewrap_unionall(tuple_tfunc(limit_tuple_depth(params,
-                                                                                            tupletype_tail(atypes, la))),
-                                                              linfo.specTypes),
+                    s_types[1][la] = VarState(rewrap(tuple_tfunc(limit_tuple_depth(params,
+                                                                                   tupletype_tail(atypes, la))),
+                                                     linfo.specTypes),
                                               false)
                 end
                 la -= 1
@@ -572,8 +577,8 @@ function getfield_tfunc(s00::ANY, name)
         end
         s = DataType # typeof(p1)
     elseif isa(s,Union)
-        return rewrap_unionall(tmerge(getfield_tfunc(s.a, name), getfield_tfunc(s.b, name)),
-                               s00)
+        return rewrap(tmerge(getfield_tfunc(s.a, name), getfield_tfunc(s.b, name)),
+                      s00)
     elseif isa(s,Const)
         sv = s.val
         if isa(name, Const)
diff --git a/base/weakkeydict.jl b/base/weakkeydict.jl
index cf7b89626c005..cd6128dea8d34 100644
--- a/base/weakkeydict.jl
+++ b/base/weakkeydict.jl
@@ -55,8 +55,7 @@ function WeakKeyDict(kv)
     try
         Base.associative_with_eltype((K, V) -> WeakKeyDict{K, V}, kv, eltype(kv))
     catch e
-        if any(x->isempty(methods(x, (typeof(kv),))), [start, next, done]) ||
-            !all(x->isa(x,Union{Tuple,Pair}),kv)
+        if !applicable(start, kv) || !all(x->isa(x,Union{Tuple,Pair}),kv)
             throw(ArgumentError("WeakKeyDict(kv): kv needs to be an iterator of tuples or pairs"))
         else
             rethrow(e)
diff --git a/src/jltypes.c b/src/jltypes.c
index 8858784830c32..eb16fa4b5ff0d 100644
--- a/src/jltypes.c
+++ b/src/jltypes.c
@@ -309,6 +309,10 @@ JL_DLLEXPORT jl_value_t *jl_type_union(jl_value_t **ts, size_t n)
 
 JL_DLLEXPORT jl_tvar_t *jl_new_typevar(jl_sym_t *name, jl_value_t *lb, jl_value_t *ub)
 {
+    if (lb != jl_bottom_type && !jl_is_type(lb) && !jl_is_typevar(lb))
+        jl_type_error_rt("TypeVar", "lower bound", (jl_value_t*)jl_type_type, lb);
+    if (ub != (jl_value_t*)jl_any_type && !jl_is_type(ub) && !jl_is_typevar(ub))
+        jl_type_error_rt("TypeVar", "upper bound", (jl_value_t*)jl_type_type, ub);
     jl_ptls_t ptls = jl_get_ptls_states();
     jl_tvar_t *tv = (jl_tvar_t*)jl_gc_alloc(ptls, sizeof(jl_tvar_t), jl_tvar_type);
     tv->name = name;
@@ -319,6 +323,8 @@ JL_DLLEXPORT jl_tvar_t *jl_new_typevar(jl_sym_t *name, jl_value_t *lb, jl_value_
 
 JL_DLLEXPORT jl_value_t *jl_type_unionall(jl_tvar_t *v, jl_value_t *body)
 {
+    if (!jl_is_type(body) && !jl_is_typevar(body))
+        jl_type_error_rt("UnionAll", "", (jl_value_t*)jl_type_type, body);
     // normalize `T where T<:S` => S
     if (body == (jl_value_t*)v)
         return v->ub;
diff --git a/test/core.jl b/test/core.jl
index dc74a02275633..921108360940f 100644
--- a/test/core.jl
+++ b/test/core.jl
@@ -10,6 +10,12 @@ f47{T}(x::Vector{Vector{T}}) = 0
 @test_throws MethodError f47(Array{Vector}(0))
 @test f47(Array{Vector{Int}}(0)) == 0
 
+# checking unionall and typevar components
+@test_throws TypeError ([] where T)
+@test_throws TypeError ([T] where T)
+@test_throws TypeError (Array{T} where T<:[])
+@test_throws TypeError (Array{T} where T>:[])
+
 # issue #8652
 args_morespecific(a, b) = ccall(:jl_type_morespecific, Cint, (Any,Any), a, b) != 0
 let
diff --git a/test/dict.jl b/test/dict.jl
index a0c7a51a6eb2f..0501d9803c92b 100644
--- a/test/dict.jl
+++ b/test/dict.jl
@@ -443,6 +443,11 @@ d = Dict(:a=>"a")
 @test_throws ArgumentError Dict([1])
 @test_throws ArgumentError Dict([(1,2),0])
 
+# test Dict constructor's argument checking (for an iterable of pairs or tuples)
+# make sure other errors can propagate when the nature of the iterator is not the problem
+@test_throws InexactError Dict(convert(Int,1.5) for i=1:1)
+@test_throws InexactError WeakKeyDict(convert(Int,1.5) for i=1:1)
+
 # ImmutableDict
 import Base.ImmutableDict
 let d = ImmutableDict{String, String}(),