diff --git a/buildstream/_loader/loader.py b/buildstream/_loader/loader.py
index b861e86..ec929ea 100644
--- a/buildstream/_loader/loader.py
+++ b/buildstream/_loader/loader.py
@@ -474,6 +474,8 @@
                 meta_element.build_dependencies.append(meta_dep)
             if dep.dep_type != 'build':
                 meta_element.dependencies.append(meta_dep)
+            if dep.strict:
+                meta_element.strict_dependencies.append(meta_dep)
 
         return meta_element
 
diff --git a/buildstream/_loader/metaelement.py b/buildstream/_loader/metaelement.py
index c13d559..370ce55 100644
--- a/buildstream/_loader/metaelement.py
+++ b/buildstream/_loader/metaelement.py
@@ -54,4 +54,5 @@
         self.sandbox = sandbox
         self.build_dependencies = []
         self.dependencies = []
+        self.strict_dependencies = []
         self.first_pass = first_pass
diff --git a/buildstream/_loader/types.py b/buildstream/_loader/types.py
index eb6932b..193fb5d 100644
--- a/buildstream/_loader/types.py
+++ b/buildstream/_loader/types.py
@@ -46,6 +46,7 @@
     DIRECTORY = "directory"
     JUNCTION = "junction"
     SANDBOX = "sandbox"
+    STRICT = "strict"
 
 
 # Dependency()
@@ -68,13 +69,14 @@
             self.name = dep
             self.dep_type = default_dep_type
             self.junction = None
+            self.strict = False
 
         elif isinstance(dep, Mapping):
             if default_dep_type:
-                _yaml.node_validate(dep, ['filename', 'junction'])
+                _yaml.node_validate(dep, ['filename', 'junction', 'strict'])
                 dep_type = default_dep_type
             else:
-                _yaml.node_validate(dep, ['filename', 'type', 'junction'])
+                _yaml.node_validate(dep, ['filename', 'type', 'junction', 'strict'])
 
                 # Make type optional, for this we set it to None
                 dep_type = _yaml.node_get(dep, str, Symbol.TYPE, default_value=None)
@@ -89,11 +91,33 @@
             self.name = _yaml.node_get(dep, str, Symbol.FILENAME)
             self.dep_type = dep_type
             self.junction = _yaml.node_get(dep, str, Symbol.JUNCTION, default_value=None)
+            self.strict = _yaml.node_get(dep, bool, Symbol.STRICT, default_value=False)
+
+            # Here we disallow explicitly setting 'strict' to False.
+            #
+            # This is in order to keep the door open to allowing the project.conf
+            # set the default of dependency 'strict'-ness which might be useful
+            # for projects which use mostly static linking and the like, in which
+            # case we can later interpret explicitly non-strict dependencies
+            # as an override of the project default.
+            #
+            if self.strict is False and Symbol.STRICT in dep:
+                provenance = _yaml.node_get_provenance(dep, key=Symbol.STRICT)
+                raise LoadError(LoadErrorReason.INVALID_DATA,
+                                "{}: Setting 'strict' to False is unsupported"
+                                .format(provenance))
 
         else:
             raise LoadError(LoadErrorReason.INVALID_DATA,
                             "{}: Dependency is not specified as a string or a dictionary".format(provenance))
 
+        # Only build dependencies are allowed to be strict
+        #
+        if self.strict and self.dep_type == Symbol.RUNTIME:
+            raise LoadError(LoadErrorReason.INVALID_DATA,
+                            "{}: Runtime dependency {} specified as `strict`.".format(self.provenance, self.name),
+                            detail="Only dependencies required at build time may be declared `strict`.")
+
         # `:` characters are not allowed in filename if a junction was
         # explicitly specified
         if self.junction and ':' in self.name:
diff --git a/buildstream/element.py b/buildstream/element.py
index 5f0e300..703f062 100644
--- a/buildstream/element.py
+++ b/buildstream/element.py
@@ -201,6 +201,7 @@
 
         self.__runtime_dependencies = []        # Direct runtime dependency Elements
         self.__build_dependencies = []          # Direct build dependency Elements
+        self.__strict_dependencies = []         # Direct build dependency subset which require strict rebuilds
         self.__reverse_dependencies = set()     # Direct reverse dependency Elements
         self.__ready_for_runtime = False        # Wether the element has all its dependencies ready and has a cache key
         self.__sources = []                     # List of Sources
@@ -939,6 +940,9 @@
             element.__build_dependencies.append(dependency)
             dependency.__reverse_dependencies.add(element)
 
+            if meta_dep in meta.strict_dependencies:
+                element.__strict_dependencies.append(dependency)
+
         return element
 
     # _get_redundant_source_refs()
@@ -1069,16 +1073,20 @@
         if self.__weak_cache_key is None:
             # Calculate weak cache key
             # Weak cache key includes names of direct build dependencies
-            # but does not include keys of dependencies.
-            if self.BST_STRICT_REBUILD:
-                dependencies = [
-                    e._get_cache_key(strength=_KeyStrength.WEAK)
-                    for e in self.dependencies(Scope.BUILD)
-                ]
-            else:
-                dependencies = [
-                    e.name for e in self.dependencies(Scope.BUILD, recurse=False)
-                ]
+            # so as to only trigger rebuilds when the shape of the
+            # dependencies change.
+            #
+            # Some conditions cause dependencies to be strict, such
+            # that this element will be rebuilt anyway if the dependency
+            # changes even in non strict mode, for these cases we just
+            # encode the dependency's weak cache key instead of it's name.
+            #
+            dependencies = [
+                e._get_cache_key(strength=_KeyStrength.WEAK)
+                if self.BST_STRICT_REBUILD or e in self.__strict_dependencies
+                else e.name
+                for e in self.dependencies(Scope.BUILD)
+            ]
 
             self.__weak_cache_key = self.__calculate_cache_key(dependencies)
 
diff --git a/doc/source/format_declaring.rst b/doc/source/format_declaring.rst
index f69d4a4..5c9d640 100644
--- a/doc/source/format_declaring.rst
+++ b/doc/source/format_declaring.rst
@@ -350,6 +350,7 @@
    - filename: foo.bst
      type: build
      junction: baseproject.bst
+     strict: false
 
 Attributes:
 
@@ -380,6 +381,16 @@
 
      The ``junction`` attribute is available since :ref:`format version 1 <project_format_version>`
 
+* ``strict``
+
+  This attribute can be used to specify that this element should
+  be rebuilt when the dependency changes, even when
+  :ref:`strict mode <user_config_strict_mode>` has been turned off.
+
+  This is appropriate whenever a dependency's output is consumed
+  verbatim in the output of the depending element, for instance
+  when static linking is in use.
+
 
 Cross-junction dependencies
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/doc/source/using_config.rst b/doc/source/using_config.rst
index c707cd0..8b6cb58 100644
--- a/doc/source/using_config.rst
+++ b/doc/source/using_config.rst
@@ -65,6 +65,8 @@
 If you give a list of URLs, earlier entries in the list will have higher
 priority than later ones.
 
+.. _user_config_strict_mode:
+
 Strict build plan
 ~~~~~~~~~~~~~~~~~
 The strict build plan option decides whether you want elements
diff --git a/tests/frontend/show.py b/tests/frontend/show.py
index 8bb0bab..92fa1f5 100644
--- a/tests/frontend/show.py
+++ b/tests/frontend/show.py
@@ -11,10 +11,8 @@
 from . import configure_project
 
 # Project directory
-DATA_DIR = os.path.join(
-    os.path.dirname(os.path.realpath(__file__)),
-    "project",
-)
+TOP_DIR = os.path.dirname(os.path.realpath(__file__))
+DATA_DIR = os.path.join(TOP_DIR, "project")
 
 
 @pytest.mark.datafiles(DATA_DIR)
@@ -371,3 +369,57 @@
     else:
         # Check that we got the explicitly set value
         assert loaded_value == int(expected_value)
+
+
+# This tests that cache keys behave as expected when
+# dependencies have been specified as `strict` and
+# when building in strict mode.
+#
+# This test will:
+#
+#  * Build the target once (and assert that it is cached)
+#  * Modify some local files which are imported
+#    by an import element which the target depends on
+#  * Assert that the cached state of the target element
+#    is as expected
+#
+# We run the test twice, once with an element which strict
+# depends on the changing import element, and one which
+# depends on it regularly.
+#
+@pytest.mark.datafiles(os.path.join(TOP_DIR, 'strict-depends'))
+@pytest.mark.parametrize("target, expected_state", [
+    ("non-strict-depends.bst", "cached"),
+    ("strict-depends.bst", "waiting"),
+])
+def test_strict_dependencies(cli, datafiles, target, expected_state):
+    project = str(datafiles)
+
+    # Configure non strict mode, this will have
+    # an effect on the build and the `bst show`
+    # commands run via cli.get_element_states()
+    cli.configure({
+        'projects': {
+            'test': {
+                'strict': False
+            }
+        }
+    })
+
+    result = cli.run(project=project, silent=True, args=['build', target])
+    result.assert_success()
+
+    states = cli.get_element_states(project, target)
+    assert states['base.bst'] == 'cached'
+    assert states[target] == 'cached'
+
+    # Now modify the file, effectively causing the common base.bst
+    # dependency to change it's cache key
+    hello_path = os.path.join(project, 'files', 'hello.txt')
+    with open(hello_path, 'w') as f:
+        f.write("Goodbye")
+
+    # Now assert that we have the states we expect as a result
+    states = cli.get_element_states(project, target)
+    assert states['base.bst'] == 'buildable'
+    assert states[target] == expected_state
diff --git a/tests/frontend/strict-depends/elements/base.bst b/tests/frontend/strict-depends/elements/base.bst
new file mode 100644
index 0000000..ed61976
--- /dev/null
+++ b/tests/frontend/strict-depends/elements/base.bst
@@ -0,0 +1,5 @@
+kind: import
+
+sources:
+- kind: local
+  path: files
diff --git a/tests/frontend/strict-depends/elements/non-strict-depends.bst b/tests/frontend/strict-depends/elements/non-strict-depends.bst
new file mode 100644
index 0000000..9ab119b
--- /dev/null
+++ b/tests/frontend/strict-depends/elements/non-strict-depends.bst
@@ -0,0 +1,4 @@
+kind: stack
+
+build-depends:
+- base.bst
diff --git a/tests/frontend/strict-depends/elements/strict-depends.bst b/tests/frontend/strict-depends/elements/strict-depends.bst
new file mode 100644
index 0000000..1e4e294
--- /dev/null
+++ b/tests/frontend/strict-depends/elements/strict-depends.bst
@@ -0,0 +1,5 @@
+kind: stack
+
+build-depends:
+- filename: base.bst
+  strict: true
diff --git a/tests/frontend/strict-depends/files/hello.txt b/tests/frontend/strict-depends/files/hello.txt
new file mode 100644
index 0000000..f621448
--- /dev/null
+++ b/tests/frontend/strict-depends/files/hello.txt
@@ -0,0 +1 @@
+pony
diff --git a/tests/frontend/strict-depends/project.conf b/tests/frontend/strict-depends/project.conf
new file mode 100644
index 0000000..6275225
--- /dev/null
+++ b/tests/frontend/strict-depends/project.conf
@@ -0,0 +1,2 @@
+name: test
+element-path: elements
diff --git a/tests/loader/dependencies.py b/tests/loader/dependencies.py
index cb750fc..e4b9c73 100644
--- a/tests/loader/dependencies.py
+++ b/tests/loader/dependencies.py
@@ -124,6 +124,28 @@
 
 
 @pytest.mark.datafiles(DATA_DIR)
+def test_invalid_strict_dependency(cli, datafiles):
+    basedir = os.path.join(datafiles.dirname, datafiles.basename)
+    loader = make_loader(basedir)
+
+    with pytest.raises(LoadError) as exc:
+        element = loader.load(['elements/invalidstrict.bst'])[0]
+
+    assert (exc.value.reason == LoadErrorReason.INVALID_DATA)
+
+
+@pytest.mark.datafiles(DATA_DIR)
+def test_invalid_non_strict_dependency(cli, datafiles):
+    basedir = os.path.join(datafiles.dirname, datafiles.basename)
+    loader = make_loader(basedir)
+
+    with pytest.raises(LoadError) as exc:
+        element = loader.load(['elements/invalidnonstrict.bst'])[0]
+
+    assert (exc.value.reason == LoadErrorReason.INVALID_DATA)
+
+
+@pytest.mark.datafiles(DATA_DIR)
 def test_build_dependency(datafiles):
     basedir = os.path.join(datafiles.dirname, datafiles.basename)
     loader = make_loader(basedir)
diff --git a/tests/loader/dependencies/elements/invalidnonstrict.bst b/tests/loader/dependencies/elements/invalidnonstrict.bst
new file mode 100644
index 0000000..3cb31a0
--- /dev/null
+++ b/tests/loader/dependencies/elements/invalidnonstrict.bst
@@ -0,0 +1,10 @@
+kind: manual
+description: |
+
+  This is an invalid non strict dependency because it is
+  currently illegal to explicitly set a dependency to be
+  non-strict (even though this is the default).
+
+depends:
+- filename: firstdep.bst
+  strict: false
diff --git a/tests/loader/dependencies/elements/invalidstrict.bst b/tests/loader/dependencies/elements/invalidstrict.bst
new file mode 100644
index 0000000..8893b4a
--- /dev/null
+++ b/tests/loader/dependencies/elements/invalidstrict.bst
@@ -0,0 +1,9 @@
+kind: manual
+description: |
+
+  This is an invalid strict dependency because runtime
+  dependencies cannot be strict.
+
+runtime-depends:
+- filename: firstdep.bst
+  strict: true