diff --git a/src/helpers.rs b/src/helpers.rs
index b71f830b2b..5217634205 100644
--- a/src/helpers.rs
+++ b/src/helpers.rs
@@ -628,6 +628,14 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         }
         Ok(())
     }
+
+    fn frame_in_std(&self) -> bool {
+        let this = self.eval_context_ref();
+        this.tcx.lang_items().start_fn().map_or(false, |start_fn| {
+            this.tcx.def_path(this.frame().instance.def_id()).krate
+                == this.tcx.def_path(start_fn).krate
+        })
+    }
 }
 
 /// Check that the number of args is what we expect.
diff --git a/src/shims/posix/foreign_items.rs b/src/shims/posix/foreign_items.rs
index a756256aab..2ecea4d9f4 100644
--- a/src/shims/posix/foreign_items.rs
+++ b/src/shims/posix/foreign_items.rs
@@ -475,7 +475,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
             // Incomplete shims that we "stub out" just to get pre-main initialization code to work.
             // These shims are enabled only when the caller is in the standard library.
             "pthread_attr_getguardsize"
-            if this.frame().instance.to_string().starts_with("std::sys::unix::") => {
+            if this.frame_in_std() => {
                 this.check_abi(abi, Abi::C { unwind: false })?;
                 let &[ref _attr, ref guard_size] = check_arg_count(args)?;
                 let guard_size = this.deref_operand(guard_size)?;
@@ -488,13 +488,13 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
             | "pthread_attr_init"
             | "pthread_attr_destroy"
-            if this.frame().instance.to_string().starts_with("std::sys::unix::") => {
+            if this.frame_in_std() => {
                 this.check_abi(abi, Abi::C { unwind: false })?;
                 let &[_] = check_arg_count(args)?;
                 this.write_null(dest)?;
             }
             | "pthread_attr_setstacksize"
-            if this.frame().instance.to_string().starts_with("std::sys::unix::") => {
+            if this.frame_in_std() => {
                 this.check_abi(abi, Abi::C { unwind: false })?;
                 let &[_, _] = check_arg_count(args)?;
                 this.write_null(dest)?;
@@ -502,14 +502,14 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
             | "signal"
             | "sigaltstack"
-            if this.frame().instance.to_string().starts_with("std::sys::unix::") => {
+            if this.frame_in_std() => {
                 this.check_abi(abi, Abi::C { unwind: false })?;
                 let &[_, _] = check_arg_count(args)?;
                 this.write_null(dest)?;
             }
             | "sigaction"
             | "mprotect"
-            if this.frame().instance.to_string().starts_with("std::sys::unix::") => {
+            if this.frame_in_std() => {
                 this.check_abi(abi, Abi::C { unwind: false })?;
                 let &[_, _, _] = check_arg_count(args)?;
                 this.write_null(dest)?;
diff --git a/src/shims/posix/linux/foreign_items.rs b/src/shims/posix/linux/foreign_items.rs
index 598d89fe1f..9017dc368b 100644
--- a/src/shims/posix/linux/foreign_items.rs
+++ b/src/shims/posix/linux/foreign_items.rs
@@ -207,9 +207,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
             // Incomplete shims that we "stub out" just to get pre-main initialization code to work.
             // These shims are enabled only when the caller is in the standard library.
-            "pthread_getattr_np"
-                if this.frame().instance.to_string().starts_with("std::sys::unix::") =>
-            {
+            "pthread_getattr_np" if this.frame_in_std() => {
                 this.check_abi(abi, Abi::C { unwind: false })?;
                 let &[ref _thread, ref _attr] = check_arg_count(args)?;
                 this.write_null(dest)?;
diff --git a/src/shims/posix/macos/foreign_items.rs b/src/shims/posix/macos/foreign_items.rs
index d54e1bfbe8..313d38c80b 100644
--- a/src/shims/posix/macos/foreign_items.rs
+++ b/src/shims/posix/macos/foreign_items.rs
@@ -149,7 +149,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
             // Incomplete shims that we "stub out" just to get pre-main initialization code to work.
             // These shims are enabled only when the caller is in the standard library.
-            "mmap" if this.frame().instance.to_string().starts_with("std::sys::unix::") => {
+            "mmap" if this.frame_in_std() => {
                 this.check_abi(abi, Abi::C { unwind: false })?;
                 // This is a horrible hack, but since the guard page mechanism calls mmap and expects a particular return value, we just give it that value.
                 let &[ref addr, _, _, _, _, _] = check_arg_count(args)?;
diff --git a/src/shims/windows/foreign_items.rs b/src/shims/windows/foreign_items.rs
index 3c7451352d..76657a5355 100644
--- a/src/shims/windows/foreign_items.rs
+++ b/src/shims/windows/foreign_items.rs
@@ -348,35 +348,27 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
             // Incomplete shims that we "stub out" just to get pre-main initialization code to work.
             // These shims are enabled only when the caller is in the standard library.
-            "GetProcessHeap"
-                if this.frame().instance.to_string().starts_with("std::sys::windows::") =>
-            {
+            "GetProcessHeap" if this.frame_in_std() => {
                 this.check_abi(abi, Abi::System { unwind: false })?;
                 let &[] = check_arg_count(args)?;
                 // Just fake a HANDLE
                 this.write_scalar(Scalar::from_machine_isize(1, this), dest)?;
             }
-            "SetConsoleTextAttribute"
-                if this.frame().instance.to_string().starts_with("std::sys::windows::") =>
-            {
+            "SetConsoleTextAttribute" if this.frame_in_std() => {
                 this.check_abi(abi, Abi::System { unwind: false })?;
                 #[allow(non_snake_case)]
                 let &[ref _hConsoleOutput, ref _wAttribute] = check_arg_count(args)?;
                 // Pretend these does not exist / nothing happened, by returning zero.
                 this.write_null(dest)?;
             }
-            "AddVectoredExceptionHandler"
-                if this.frame().instance.to_string().starts_with("std::sys::windows::") =>
-            {
+            "AddVectoredExceptionHandler" if this.frame_in_std() => {
                 this.check_abi(abi, Abi::System { unwind: false })?;
                 #[allow(non_snake_case)]
                 let &[ref _First, ref _Handler] = check_arg_count(args)?;
                 // Any non zero value works for the stdlib. This is just used for stack overflows anyway.
                 this.write_scalar(Scalar::from_machine_usize(1, this), dest)?;
             }
-            "SetThreadStackGuarantee"
-                if this.frame().instance.to_string().starts_with("std::sys::windows::") =>
-            {
+            "SetThreadStackGuarantee" if this.frame_in_std() => {
                 this.check_abi(abi, Abi::System { unwind: false })?;
                 #[allow(non_snake_case)]
                 let &[_StackSizeInBytes] = check_arg_count(args)?;
@@ -387,7 +379,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
             | "EnterCriticalSection"
             | "LeaveCriticalSection"
             | "DeleteCriticalSection"
-                if this.frame().instance.to_string().starts_with("std::sys::windows::") =>
+                if this.frame_in_std() =>
             {
                 this.check_abi(abi, Abi::System { unwind: false })?;
                 #[allow(non_snake_case)]
@@ -401,9 +393,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 // (Windows locks are reentrant, and we have only 1 thread,
                 // so not doing any futher checks here is at least not incorrect.)
             }
-            "TryEnterCriticalSection"
-                if this.frame().instance.to_string().starts_with("std::sys::windows::") =>
-            {
+            "TryEnterCriticalSection" if this.frame_in_std() => {
                 this.check_abi(abi, Abi::System { unwind: false })?;
                 #[allow(non_snake_case)]
                 let &[ref _lpCriticalSection] = check_arg_count(args)?;
diff --git a/tests/compile-fail/unsupported_signal.rs b/tests/compile-fail/unsupported_signal.rs
new file mode 100644
index 0000000000..3e76d1c3f3
--- /dev/null
+++ b/tests/compile-fail/unsupported_signal.rs
@@ -0,0 +1,13 @@
+//! `signal()` is special on Linux and macOS that it's only supported within libstd.
+//! The implementation is not complete enough to permit user code to call it.
+// ignore-windows: No libc on Windows
+#![feature(rustc_private)]
+
+extern crate libc;
+
+fn main() {
+    unsafe {
+        libc::signal(libc::SIGPIPE, libc::SIG_IGN);
+        //~^ ERROR unsupported operation: can't call foreign function: signal
+    }
+}
diff --git a/tests/run-pass/extern_crate_std_in_main.rs b/tests/run-pass/extern_crate_std_in_main.rs
new file mode 100644
index 0000000000..8f71e61337
--- /dev/null
+++ b/tests/run-pass/extern_crate_std_in_main.rs
@@ -0,0 +1,5 @@
+#![no_std]
+
+fn main() {
+    extern crate std;
+}
diff --git a/tests/run-pass/rename_std.rs b/tests/run-pass/rename_std.rs
new file mode 100644
index 0000000000..7e82e53e6b
--- /dev/null
+++ b/tests/run-pass/rename_std.rs
@@ -0,0 +1,5 @@
+#![no_std]
+
+extern crate std as foo;
+
+fn main() {}