diff --git a/mistral/tests/unit/workbook/v2/test_dsl_specs_v2.py b/mistral/tests/unit/workbook/v2/test_dsl_specs_v2.py
index 03032a0d2..dd4f47b06 100644
--- a/mistral/tests/unit/workbook/v2/test_dsl_specs_v2.py
+++ b/mistral/tests/unit/workbook/v2/test_dsl_specs_v2.py
@@ -105,7 +105,7 @@ workflows:
 
       task7:
         with-items: vm_info in $.vms
-        workflow: wf2 is_true=true object_list=[1, null, "str"]
+        workflow: wf2 is_true=true object_list=[1, null, "str"] is_string="50"
         on-complete:
           - task9
           - task10
@@ -327,6 +327,7 @@ class DSLv2ModelTest(base.BaseTest):
             {
                 'is_true': True,
                 'object_list': [1, None, 'str'],
+                'is_string': '50'
             },
             task7_spec.get_input()
         )
diff --git a/mistral/workbook/base.py b/mistral/workbook/base.py
index d97a86543..a56a3aec3 100644
--- a/mistral/workbook/base.py
+++ b/mistral/workbook/base.py
@@ -21,8 +21,22 @@ from mistral import exceptions as exc
 
 
 CMD_PTRN = re.compile("^[\w\.]+[^=\s\"]*")
-PARAMS_PTRN = re.compile("([\w]+)=(\"[^\"]*\"\s*|'[^']*'\s*|"
-                         "\{[^}]*\}\s*|\[.*\]\s*|[\.,:\w\d\.]+)")
+
+_ALL_IN_BRACES = "\{[^}]*\}\s*"
+_ALL_IN_BRACKETS = "\[.*\]\s*"
+_ALL_IN_QUOTES = "\"[^\"]*\"\s*"
+_ALL_IN_APOSTROPHES = "'[^']*'\s*"
+_DIGITS = "\d+"
+_TRUE = "true"
+_FALSE = "false"
+_NULL = "null"
+
+ALL = (
+    _ALL_IN_QUOTES, _ALL_IN_APOSTROPHES, _ALL_IN_BRACES,
+    _ALL_IN_BRACKETS, _TRUE, _FALSE, _NULL, _DIGITS
+)
+
+PARAMS_PTRN = re.compile("([\w]+)=(%s)" % "|".join(ALL))
 
 
 class BaseSpec(object):