diff --git a/.github/workflows/IntegrationTest.yml b/.github/workflows/IntegrationTest.yml
index a15cf6e8e..28ed3570a 100644
--- a/.github/workflows/IntegrationTest.yml
+++ b/.github/workflows/IntegrationTest.yml
@@ -24,7 +24,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: julia-actions/setup-julia@v1
         with:
-          version: 1
+          version: 1.5
           arch: x64
       - uses: julia-actions/julia-buildpkg@latest
       - name: Clone Downstream
diff --git a/Project.toml b/Project.toml
index 4b5926753..ec9ef4e96 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "DynamicPPL"
 uuid = "366bfd00-2699-11ea-058f-f148b4cae6d8"
-version = "0.10.11"
+version = "0.10.12"
 
 [deps]
 AbstractMCMC = "80f14c24-f653-4e6a-9b94-39d6b0f70001"
diff --git a/src/compiler.jl b/src/compiler.jl
index 1de89ef3d..a70401bfa 100644
--- a/src/compiler.jl
+++ b/src/compiler.jl
@@ -72,7 +72,7 @@ function model(mod, linenumbernode, expr, warn)
 
     # Generate main body
     modelinfo[:body] = generate_mainbody(
-        mod, modelinfo[:modeldef][:body], modelinfo[:allargs_syms], warn
+        mod, modelinfo[:modeldef][:body], warn
     )
 
     return build_output(modelinfo, linenumbernode)
@@ -155,7 +155,7 @@ function build_model_info(input_expr)
 end
 
 """
-    generate_mainbody(mod, expr, args, warn)
+    generate_mainbody(mod, expr, warn)
 
 Generate the body of the main evaluation function from expression `expr` and arguments
 `args`.
@@ -163,84 +163,76 @@ Generate the body of the main evaluation function from expression `expr` and arg
 If `warn` is true, a warning is displayed if internal variables are used in the model
 definition.
 """
-generate_mainbody(mod, expr, args, warn) = generate_mainbody!(mod, Symbol[], expr, args, warn)
+generate_mainbody(mod, expr, warn) = generate_mainbody!(mod, Symbol[], expr, warn)
 
-generate_mainbody!(mod, found, x, args, warn) = x
-function generate_mainbody!(mod, found, sym::Symbol, args, warn)
+generate_mainbody!(mod, found, x, warn) = x
+function generate_mainbody!(mod, found, sym::Symbol, warn)
     if warn && sym in INTERNALNAMES && sym ∉ found
         @warn "you are using the internal variable `$(sym)`"
         push!(found, sym)
     end
     return sym
 end
-function generate_mainbody!(mod, found, expr::Expr, args, warn)
+function generate_mainbody!(mod, found, expr::Expr, warn)
     # Do not touch interpolated expressions
     expr.head === :$ && return expr.args[1]
 
     # If it's a macro, we expand it
     if Meta.isexpr(expr, :macrocall)
-        return generate_mainbody!(mod, found, macroexpand(mod, expr; recursive=true), args, warn)
+        return generate_mainbody!(mod, found, macroexpand(mod, expr; recursive=true), warn)
     end
 
     # Modify dotted tilde operators.
     args_dottilde = getargs_dottilde(expr)
     if args_dottilde !== nothing
         L, R = args_dottilde
-        return generate_dot_tilde(generate_mainbody!(mod, found, L, args, warn),
-                                  generate_mainbody!(mod, found, R, args, warn),
-                                  args) |> Base.remove_linenums!
+        return generate_dot_tilde(
+            generate_mainbody!(mod, found, L, warn),
+            generate_mainbody!(mod, found, R, warn),
+        ) |> Base.remove_linenums!
     end
 
     # Modify tilde operators.
     args_tilde = getargs_tilde(expr)
     if args_tilde !== nothing
         L, R = args_tilde
-        return generate_tilde(generate_mainbody!(mod, found, L, args, warn),
-                              generate_mainbody!(mod, found, R, args, warn),
-                              args) |> Base.remove_linenums!
+        return generate_tilde(
+            generate_mainbody!(mod, found, L, warn),
+            generate_mainbody!(mod, found, R, warn),
+        ) |> Base.remove_linenums!
     end
 
-    return Expr(expr.head, map(x -> generate_mainbody!(mod, found, x, args, warn), expr.args)...)
+    return Expr(expr.head, map(x -> generate_mainbody!(mod, found, x, warn), expr.args)...)
 end
 
 
 
 """
-    generate_tilde(left, right, args)
+    generate_tilde(left, right)
 
 Generate an `observe` expression for data variables and `assume` expression for parameter
 variables.
 """
-function generate_tilde(left, right, args)
+function generate_tilde(left, right)
     @gensym tmpright
     top = [:($tmpright = $right),
            :($tmpright isa Union{$Distribution,AbstractVector{<:$Distribution}}
              || throw(ArgumentError($DISTMSG)))]
 
     if left isa Symbol || left isa Expr
-        @gensym out vn inds
+        @gensym out vn inds isassumption
         push!(top, :($vn = $(varname(left))), :($inds = $(vinds(left))))
 
-        # It can only be an observation if the LHS is an argument of the model
-        if vsym(left) in args
-            @gensym isassumption
-            return quote
-                $(top...)
-                $isassumption = $(DynamicPPL.isassumption(left))
-                if $isassumption
-                    $left = $(DynamicPPL.tilde_assume)(
-                        _rng, _context, _sampler, $tmpright, $vn, $inds, _varinfo)
-                else
-                    $(DynamicPPL.tilde_observe)(
-                        _context, _sampler, $tmpright, $left, $vn, $inds, _varinfo)
-                end
-            end
-        end
-
         return quote
             $(top...)
-            $left = $(DynamicPPL.tilde_assume)(_rng, _context, _sampler, $tmpright, $vn,
-                                               $inds, _varinfo)
+            $isassumption = $(DynamicPPL.isassumption(left))
+            if $isassumption
+                $left = $(DynamicPPL.tilde_assume)(
+                    _rng, _context, _sampler, $tmpright, $vn, $inds, _varinfo)
+            else
+                $(DynamicPPL.tilde_observe)(
+                    _context, _sampler, $tmpright, $left, $vn, $inds, _varinfo)
+            end
         end
     end
 
@@ -252,40 +244,30 @@ function generate_tilde(left, right, args)
 end
 
 """
-    generate_dot_tilde(left, right, args)
+    generate_dot_tilde(left, right)
 
 Generate the expression that replaces `left .~ right` in the model body.
 """
-function generate_dot_tilde(left, right, args)
+function generate_dot_tilde(left, right)
     @gensym tmpright
     top = [:($tmpright = $right),
            :($tmpright isa Union{$Distribution,AbstractVector{<:$Distribution}}
              || throw(ArgumentError($DISTMSG)))]
 
     if left isa Symbol || left isa Expr
-        @gensym out vn inds
+        @gensym out vn inds isassumption
         push!(top, :($vn = $(varname(left))), :($inds = $(vinds(left))))
 
-        # It can only be an observation if the LHS is an argument of the model
-        if vsym(left) in args
-            @gensym isassumption
-            return quote
-                $(top...)
-                $isassumption = $(DynamicPPL.isassumption(left))
-                if $isassumption
-                    $left .= $(DynamicPPL.dot_tilde_assume)(
-                        _rng, _context, _sampler, $tmpright, $left, $vn, $inds, _varinfo)
-                else
-                    $(DynamicPPL.dot_tilde_observe)(
-                        _context, _sampler, $tmpright, $left, $vn, $inds, _varinfo)
-                end
-            end
-        end
-
         return quote
             $(top...)
-            $left .= $(DynamicPPL.dot_tilde_assume)(
-                _rng, _context, _sampler, $tmpright, $left, $vn, $inds, _varinfo)
+            $isassumption = $(DynamicPPL.isassumption(left)) || $left === missing
+            if $isassumption
+                $left .= $(DynamicPPL.dot_tilde_assume)(
+                    _rng, _context, _sampler, $tmpright, $left, $vn, $inds, _varinfo)
+            else
+                $(DynamicPPL.dot_tilde_observe)(
+                    _context, _sampler, $tmpright, $left, $vn, $inds, _varinfo)
+            end
         end
     end