diff --git a/functions-common b/functions-common
index e48ceaf341..48edba8da6 100644
--- a/functions-common
+++ b/functions-common
@@ -1645,6 +1645,16 @@ function setup_develop {
     setup_package_with_req_sync $project_dir -e
 }
 
+# determine if a project as specified by directory is in
+# projects.txt. This will not be an exact match because we throw away
+# the namespacing when we clone, but it should be good enough in all
+# practical ways.
+function is_in_projects_txt {
+    local project_dir=$1
+    local project_name=$(basename $project_dir)
+    return grep "/$project_name\$" $REQUIREMENTS_DIR/projects.txt >/dev/null
+}
+
 # ``pip install -e`` the package, which processes the dependencies
 # using pip before running `setup.py develop`
 #
@@ -1663,8 +1673,19 @@ function setup_package_with_req_sync {
     local update_requirements=$(cd $project_dir && git diff --exit-code >/dev/null || echo "changed")
 
     if [[ $update_requirements != "changed" ]]; then
-        (cd $REQUIREMENTS_DIR; \
-            python update.py $project_dir)
+        if [[ "$REQUIREMENTS_MODE" == "soft" ]]; then
+            if is_in_projects_txt $project_dir; then
+                (cd $REQUIREMENTS_DIR; \
+                    python update.py $project_dir)
+            else
+                # soft update projects not found in requirements project.txt
+                (cd $REQUIREMENTS_DIR; \
+                    python update.py -s $project_dir)
+            fi
+        else
+            (cd $REQUIREMENTS_DIR; \
+                python update.py $project_dir)
+        fi
     fi
 
     setup_package $project_dir $flags
diff --git a/stackrc b/stackrc
index fd84598c5f..15b0951a1a 100644
--- a/stackrc
+++ b/stackrc
@@ -116,6 +116,17 @@ DATABASE_QUERY_LOGGING=$(trueorfalse True $DATABASE_QUERY_LOGGING)
 # Zero disables timeouts
 GIT_TIMEOUT=${GIT_TIMEOUT:-0}
 
+# Requirements enforcing mode
+#
+# - strict (default) : ensure all project requirements files match
+#   what's in global requirements.
+#
+# - soft : enforce requirements on everything in
+#   requirements/projects.txt, but do soft updates on all other
+#   repositories (i.e. sync versions for requirements that are in g-r,
+#   but pass through any extras)
+REQUIREMENTS_MODE=${REQUIREMENTS_MODE:-strict}
+
 # Repositories
 # ------------