diff --git a/rust-version b/rust-version
index 1733872825..9e4ddf2aca 100644
--- a/rust-version
+++ b/rust-version
@@ -1 +1 @@
-7e08576e4276a97b523c25bfd196d419c39c7b87
+088b987307b91612ab164026e1dcdd0129fdb62b
diff --git a/src/eval.rs b/src/eval.rs
index a1157af0e3..91a563fa56 100644
--- a/src/eval.rs
+++ b/src/eval.rs
@@ -35,8 +35,16 @@ pub fn create_ecx<'mir, 'tcx: 'mir>(
         Evaluator::new(),
     );
 
+    // FIXME(https://github.com/rust-lang/miri/pull/803): no validation on Windows.
+    let target_os = ecx.tcx.tcx.sess.target.target.target_os.to_lowercase();
+    let validate = if target_os == "windows" {
+        false
+    } else {
+        config.validate
+    };
+
     // FIXME: InterpretCx::new should take an initial MemoryExtra
-    ecx.memory_mut().extra = MemoryExtra::new(config.seed.map(StdRng::seed_from_u64), config.validate);
+    ecx.memory_mut().extra = MemoryExtra::new(config.seed.map(StdRng::seed_from_u64), validate);
     
     let main_instance = ty::Instance::mono(ecx.tcx.tcx, main_id);
     let main_mir = ecx.load_mir(main_instance.def)?;
diff --git a/src/shims/foreign_items.rs b/src/shims/foreign_items.rs
index d43374f1bc..2a3644e45c 100644
--- a/src/shims/foreign_items.rs
+++ b/src/shims/foreign_items.rs
@@ -50,8 +50,9 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
     ) -> InterpResult<'tcx> {
         let this = self.eval_context_mut();
         if !this.is_null(ptr)? {
+            let ptr = this.force_ptr(ptr)?;
             this.memory_mut().deallocate(
-                ptr.to_ptr()?,
+                ptr,
                 None,
                 MiriMemoryKind::C.into(),
             )?;
@@ -78,7 +79,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 Ok(Scalar::Ptr(new_ptr))
             }
         } else {
-            let old_ptr = old_ptr.to_ptr()?;
+            let old_ptr = this.force_ptr(old_ptr)?;
             let memory = this.memory_mut();
             let old_size = Size::from_bytes(memory.get(old_ptr.alloc_id)?.bytes.len() as u64);
             if new_size == 0 {
@@ -234,7 +235,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 this.write_scalar(Scalar::Ptr(ptr), dest)?;
             }
             "__rust_dealloc" => {
-                let ptr = this.read_scalar(args[0])?.to_ptr()?;
+                let ptr = this.read_scalar(args[0])?.not_undef()?;
                 let old_size = this.read_scalar(args[1])?.to_usize(this)?;
                 let align = this.read_scalar(args[2])?.to_usize(this)?;
                 if old_size == 0 {
@@ -243,6 +244,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 if !align.is_power_of_two() {
                     return err!(HeapAllocNonPowerOfTwoAlignment(align));
                 }
+                let ptr = this.force_ptr(ptr)?;
                 this.memory_mut().deallocate(
                     ptr,
                     Some((Size::from_bytes(old_size), Align::from_bytes(align).unwrap())),
diff --git a/test-cargo-miri/run-test.py b/test-cargo-miri/run-test.py
index 73515c74e4..a9aba008e9 100755
--- a/test-cargo-miri/run-test.py
+++ b/test-cargo-miri/run-test.py
@@ -52,8 +52,9 @@ def test_cargo_miri_run():
     )
 
 def test_cargo_miri_test():
+    # FIXME: enable validation again, once that no longer conflicts with intptrcast
     test("cargo miri test",
-        cargo_miri("test") + ["--", "-Zmiri-seed=feed"],
+        cargo_miri("test") + ["--", "-Zmiri-seed=feed", "-Zmiri-disable-validation"],
         "test.stdout.ref", "test.stderr.ref"
     )
     test("cargo miri test (with filter)",
diff --git a/tests/compiletest.rs b/tests/compiletest.rs
index 1d32d3a732..076deca6a3 100644
--- a/tests/compiletest.rs
+++ b/tests/compiletest.rs
@@ -112,7 +112,9 @@ fn run_pass_miri(opt: bool) {
 }
 
 fn compile_fail_miri(opt: bool) {
-    compile_fail("tests/compile-fail", &get_target(), opt);
+    if !cfg!(windows) { // FIXME re-enable on Windows
+        compile_fail("tests/compile-fail", &get_target(), opt);
+    }
 }
 
 fn test_runner(_tests: &[&()]) {
diff --git a/tests/run-pass-noseed/intptrcast.rs b/tests/run-pass-noseed/intptrcast.rs
index 40b21f9a47..1b5251c911 100644
--- a/tests/run-pass-noseed/intptrcast.rs
+++ b/tests/run-pass-noseed/intptrcast.rs
@@ -1,8 +1,13 @@
 // compile-flags: -Zmiri-seed=0000000000000000
 
+// This returns a miri pointer at type usize, if the argument is a proper pointer
+fn transmute_ptr_to_int<T>(x: *const T) -> usize {
+    unsafe { std::mem::transmute(x) }
+}
+
 fn main() {
     // Some casting-to-int with arithmetic.
-    let x = &42 as *const i32 as usize; 
+    let x = &42 as *const i32 as usize;
     let y = x * 2;
     assert_eq!(y, x + x);
     let z = y as u8 as usize;
@@ -11,4 +16,11 @@ fn main() {
     // Pointer string formatting! We can't check the output as it changes when libstd changes,
     // but we can make sure Miri does not error.
     format!("{:?}", &mut 13 as *mut _);
+
+    // Check that intptrcast is triggered for explicit casts and that it is consistent with
+    // transmuting.
+    let a: *const i32 = &42;
+    let b = transmute_ptr_to_int(a) as u8;
+    let c = a as usize as u8;
+    assert_eq!(b, c);
 }
diff --git a/tests/run-pass-noseed/ptr_int_casts.rs b/tests/run-pass-noseed/ptr_int_casts.rs
index c279024f35..ebf65ac3fe 100644
--- a/tests/run-pass-noseed/ptr_int_casts.rs
+++ b/tests/run-pass-noseed/ptr_int_casts.rs
@@ -1,3 +1,4 @@
+// FIXME move this to run-pass, it should work with intptrcast.
 use std::mem;
 use std::ptr;
 
diff --git a/tests/run-pass/ptr_offset.rs b/tests/run-pass-noseed/ptr_offset.rs
similarity index 85%
rename from tests/run-pass/ptr_offset.rs
rename to tests/run-pass-noseed/ptr_offset.rs
index 1c7f0eb717..a836e02812 100644
--- a/tests/run-pass/ptr_offset.rs
+++ b/tests/run-pass-noseed/ptr_offset.rs
@@ -1,3 +1,5 @@
+// FIXME move this to run-pass, it should work with intptrcast.
+
 fn f() -> i32 { 42 }
 
 fn main() {