diff --git a/giftwrap/builders/__init__.py b/giftwrap/builders/__init__.py
index f53ec9b..090f3f6 100644
--- a/giftwrap/builders/__init__.py
+++ b/giftwrap/builders/__init__.py
@@ -112,7 +112,7 @@ class Builder(object):
             if project.postinstall_dependencies:
                 dependencies = project.postinstall_dependencies
                 self._install_pip_dependencies(project.install_path,
-                                               dependencies)
+                                               dependencies, False)
 
             # finish up
             self._finalize_project_build(project)
@@ -188,7 +188,8 @@ class Builder(object):
         return
 
     @abstractmethod
-    def _install_pip_dependencies(self, venv_path, dependencies):
+    def _install_pip_dependencies(self, venv_path, dependencies,
+                                  use_constraints=True):
         return
 
     @abstractmethod
diff --git a/giftwrap/builders/docker_builder.py b/giftwrap/builders/docker_builder.py
index 7fc4629..3c4ce0c 100644
--- a/giftwrap/builders/docker_builder.py
+++ b/giftwrap/builders/docker_builder.py
@@ -82,11 +82,14 @@ class DockerBuilder(Builder):
     def _create_virtualenv(self, venv_command, path):
         self._execute(venv_command, path)
 
-    def _install_pip_dependencies(self, venv_path, dependencies):
+    def _install_pip_dependencies(self, venv_path, dependencies,
+                                  use_constraints=True):
         pip_path = self._get_venv_pip_path(venv_path)
         install = "install"
-        for constraint in self._constraints:
-            install = "%s -c %s" % (install, constraint)
+        if use_constraints:
+            for constraint in self._constraints:
+                install = "%s -c %s" % (install, constraint)
+
         for dependency in dependencies:
             self._execute("%s %s %s" % (pip_path, install, dependency))
 
diff --git a/giftwrap/builders/package_builder.py b/giftwrap/builders/package_builder.py
index f482885..bdc8ac6 100644
--- a/giftwrap/builders/package_builder.py
+++ b/giftwrap/builders/package_builder.py
@@ -68,11 +68,14 @@ class PackageBuilder(Builder):
     def _create_virtualenv(self, venv_command, path):
         self._execute(venv_command, path)
 
-    def _install_pip_dependencies(self, venv_path, dependencies):
+    def _install_pip_dependencies(self, venv_path, dependencies,
+                                  use_constraints=True):
         pip_path = self._get_venv_pip_path(venv_path)
         install = "install"
-        for constraint in self._constraints:
-            install = "%s -c %s" % (install, constraint)
+        if use_constraints:
+            for constraint in self._constraints:
+                install = "%s -c %s" % (install, constraint)
+
         for dependency in dependencies:
             self._execute("%s %s %s" % (pip_path, install, dependency))