--- a/build/moz.configure/toolchain.configure
+++ b/build/moz.configure/toolchain.configure
@@ -1479,18 +1479,18 @@ imply_option('RUSTC_OPT_LEVEL', '2', whe
 @depends('RUSTC_OPT_LEVEL', moz_optimize)
 def rustc_opt_level(opt_level_option, moz_optimize):
     if opt_level_option:
         return opt_level_option[0]
     else:
         return '1' if moz_optimize.optimize else '0'
 
 
-@depends(rustc_opt_level, debug_rust, '--enable-debug-symbols')
-def rust_compiler_flags(opt_level, debug_rust, debug_symbols):
+@depends(rustc_opt_level, debug_rust, '--enable-debug-symbols', cross_compiling, target)
+def rust_compiler_flags(opt_level, debug_rust, debug_symbols, cross_compiling, target):
     # Cargo currently supports only two interesting profiles for building:
     # development and release. Those map (roughly) to --enable-debug and
     # --disable-debug in Gecko, respectively.
     #
     # But we'd also like to support an additional axis of control for
     # optimization level. Since Cargo only supports 2 profiles, we're in
     # a bit of a bind.
     #
@@ -1518,16 +1518,21 @@ def rust_compiler_flags(opt_level, debug
                     ('yes' if debug_assertions else 'no'))
     if debug_info is not None:
         opts.append('debuginfo=%s' % debug_info)
 
     flags = []
     for opt in opts:
         flags.extend(['-C', opt])
 
+    # When cross-compiling for mac, rustc will try to run dsymutil after linking binaries,
+    # and we don't have that in PATH.
+    if target.os == 'OSX' and cross_compiling:
+        flags.extend(('-Z', 'run-dsymutil=no'))
+
     return flags
 
 
 set_config('MOZ_RUST_DEFAULT_FLAGS', rust_compiler_flags)
 
 # Rust incremental compilation
 # ==============================================================
 

--- a/config/rules.mk
+++ b/config/rules.mk
@@ -881,17 +881,17 @@ environment_cleaner = -u VCINSTALLDIR PA
 # The servo build needs to know where python is, and we're removing the PATH
 # so we tell it explicitly via the PYTHON env var.
 environment_cleaner += PYTHON='$(shell which $(PYTHON))'
 else
 environment_cleaner =
 endif
 
 rust_unlock_unstable =
-ifdef MOZ_RUST_SIMD
+ifdef MOZ_RUSTC_BOOSTRAP
 rust_unlock_unstable += RUSTC_BOOTSTRAP=1
 endif
 
 ifdef MOZ_USING_SCCACHE
 sccache_wrap := RUSTC_WRAPPER='$(CCACHE)'
 endif
 
 ifneq (WINNT,$(OS_ARCH))

--- a/toolkit/moz.configure
+++ b/toolkit/moz.configure
@@ -850,16 +850,26 @@ def rust_simd(value, target):
     # As of 2018-06-05, the simd crate only works on aarch64,
     # armv7, x86 and x86_64.
     if target.cpu in ('aarch64', 'arm', 'x86', 'x86_64') and value:
         return True
 
 set_config('MOZ_RUST_SIMD', rust_simd)
 set_define('MOZ_RUST_SIMD', rust_simd)
 
+
+@depends(cross_compiling, target, rust_simd)
+def rustc_bootstrap(cross_compiling, target, rust_simd):
+    # We need to unlock unstable rustc features if we're using simd or
+    # cross-compiling a mac build.
+    if rust_simd or (target.os == 'OSX' and cross_compiling):
+        return True
+
+set_config('MOZ_RUSTC_BOOSTRAP', rustc_bootstrap)
+
 # Printing
 # ==============================================================
 @depends(target)
 def ios_disable_printing(target):
     if target.os == 'iOS':
         return False
 
 imply_option('--enable-printing', ios_disable_printing, reason='--target')