--- a/build/moz.configure/toolchain.configure
+++ b/build/moz.configure/toolchain.configure
@@ -3,29 +3,28 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 # yasm detection
 # ==============================================================
 yasm = check_prog('YASM', ['yasm'], allow_missing=True)
 
-@depends(yasm)
+@depends_true(yasm)
 @checking('yasm version')
 @advanced
 def yasm_version(yasm):
-    if yasm:
-        import subprocess
-        try:
-            version = Version(subprocess.check_output(
-                [yasm, '--version']
-            ).splitlines()[0].split()[1])
-            return version
-        except subprocess.CalledProcessError as e:
-            error('Failed to get yasm version: %s' % e.message)
+    import subprocess
+    try:
+        version = Version(subprocess.check_output(
+            [yasm, '--version']
+        ).splitlines()[0].split()[1])
+        return version
+    except subprocess.CalledProcessError as e:
+        error('Failed to get yasm version: %s' % e.message)
 
 # Until we move all the yasm consumers out of old-configure.
 # bug 1257904
 add_old_configure_assignment('_YASM_MAJOR_VERSION',
                              delayed_getattr(yasm_version, 'major'))
 add_old_configure_assignment('_YASM_MINOR_VERSION',
                              delayed_getattr(yasm_version, 'minor'))
 

--- a/build/moz.configure/util.configure
+++ b/build/moz.configure/util.configure
@@ -125,8 +125,21 @@ def delayed_getattr(func, key):
         try:
             return getattr(value, key)
         except AttributeError:
             # The @depends function we're being passed may have returned
             # None, or an object that simply doesn't have the wanted key.
             # In that case, just return None.
             return None
     return result
+
+
+# Like @depends, but the decorated function is only called if one of the
+# arguments it would be called with has a positive value (bool(value) is True)
+@template
+def depends_true(*args):
+    def decorator(func):
+        @depends(*args)
+        def wrapper(*args):
+            if any(arg for arg in args):
+                return func(*args)
+        return wrapper
+    return decorator