diff --git a/src/librustc_driver/driver.rs b/src/librustc_driver/driver.rs
index c592882a1e4..68e6b0f50d1 100644
--- a/src/librustc_driver/driver.rs
+++ b/src/librustc_driver/driver.rs
@@ -925,6 +925,10 @@ pub fn phase_3_run_analysis_passes<'tcx, F, R>(sess: &'tcx Session,
     let mut passes = Passes::new();
     passes.push_hook(mir::transform::dump_mir::DumpMir);
 
+    // Insert AcquireValid and ReleaseValid calls.  Conceptually, this
+    // pass is actually part of MIR building.
+    passes.push_pass(MIR_CONST, mir::transform::add_validation::AddValidation);
+
     // Remove all `EndRegion` statements that are not involved in borrows.
     passes.push_pass(MIR_CONST, mir::transform::clean_end_regions::CleanEndRegions);
 
diff --git a/src/librustc_mir/transform/add_validation.rs b/src/librustc_mir/transform/add_validation.rs
new file mode 100644
index 00000000000..6934ec7a74f
--- /dev/null
+++ b/src/librustc_mir/transform/add_validation.rs
@@ -0,0 +1,43 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! This pass adds validation calls (AcquireValid, ReleaseValid) where appropriate.
+//! It has to be run really early, before transformations like inlining, because
+//! introducing these calls *adds* UB -- so, conceptually, this pass is actually part
+//! of MIR building, and only after this pass we think of the program has having the
+//! normal MIR semantics.
+
+use rustc::ty::TyCtxt;
+use rustc::mir::*;
+use rustc::mir::transform::{MirPass, MirSource};
+
+pub struct AddValidation;
+
+impl MirPass for AddValidation {
+    fn run_pass<'a, 'tcx>(&self,
+                          _tcx: TyCtxt<'a, 'tcx, 'tcx>,
+                          _: MirSource,
+                          mir: &mut Mir<'tcx>) {
+        // Add an AcquireValid at the beginning of the start block
+        if mir.arg_count > 0 {
+            let acquire_stmt = Statement {
+                source_info: SourceInfo {
+                    scope: ARGUMENT_VISIBILITY_SCOPE,
+                    span: mir.span,
+                },
+                kind: StatementKind::Validate(ValidationOp::Acquire,
+                    // Skip return value, go over all the arguments
+                    mir.local_decls.iter_enumerated().skip(1).take(mir.arg_count)
+                    .map(|(local, local_decl)| (local_decl.ty, Lvalue::Local(local))).collect())
+            };
+            mir.basic_blocks_mut()[START_BLOCK].statements.insert(0, acquire_stmt);
+        }
+    }
+}
diff --git a/src/librustc_mir/transform/mod.rs b/src/librustc_mir/transform/mod.rs
index c9c8ad0e0eb..a247ce2231e 100644
--- a/src/librustc_mir/transform/mod.rs
+++ b/src/librustc_mir/transform/mod.rs
@@ -24,6 +24,7 @@ use syntax::ast;
 use syntax_pos::{DUMMY_SP, Span};
 use transform;
 
+pub mod add_validation;
 pub mod clean_end_regions;
 pub mod simplify_branches;
 pub mod simplify;