diff --git a/gui/wxpython/gmodeler/model.py b/gui/wxpython/gmodeler/model.py
index 1d75f3869df..a41fd88e000 100644
--- a/gui/wxpython/gmodeler/model.py
+++ b/gui/wxpython/gmodeler/model.py
@@ -486,7 +486,8 @@ def Validate(self):
                 sval = pattern.search(value)
                 if not sval:
                     continue
-                var = sval.group(2).strip()[2:-1]  # strip '%{...}'
+                s = sval.group(2).strip()
+                var = s[2:-1] if s.startswith("%{") else s[1:]  # strip curly braces only if present
                 found = False
                 for v in variables:
                     if var.startswith(v):
@@ -539,7 +540,8 @@ def _substituteFile(self, item, params=None, checkOnly=False):
             write = False
             variables = self.GetVariables()
             for variable in variables:
-                pattern = re.compile("%{" + variable + "}")
+                # curly braces are optional
+                pattern = re.compile(r"%(?:\{" + variable + r"\}|" + variable + r")")
                 value = ""
                 if params and "variables" in params:
                     for p in params["variables"]["params"]:
@@ -560,7 +562,8 @@ def _substituteFile(self, item, params=None, checkOnly=False):
             pattern = re.compile(r"(.*)(%\{.+})(.*)")
             sval = pattern.search(data)
             if sval:
-                var = sval.group(2).strip()[2:-1]  # ignore '%{...}'
+                s = sval.group(2).strip()
+                var = s[2:-1] if s.startswith("%{") else s[1:]  # strip curly braces only if present
                 cmd = item.GetLog(string=False)[0]
                 errList.append(cmd + ": " + _("undefined variable '%s'") % var)
 
@@ -690,7 +693,8 @@ def Run(self, log, onDone, parent=None):
                 # substitute variables in condition
                 variables = self.GetVariables()
                 for variable in variables:
-                    pattern = re.compile("%{" + variable + "}")
+                    # curly braces are optional
+                    pattern = re.compile(r"%(?:\{" + variable + r"\}|" + variable + r")")
                     if not pattern.search(cond):
                         continue
                     value = ""
@@ -713,7 +717,8 @@ def Run(self, log, onDone, parent=None):
                 # split condition
                 # TODO: this part needs some better solution
                 condVar, condText = (x.strip() for x in re.split(r"\s* in \s*", cond))
-                pattern = re.compile("%{" + condVar + "}")
+                # curly braces are optional
+                pattern = re.compile(r"%(?:\{" + condVar + r"\}|" + condVar + r")")
                 # for vars()[condVar] in eval(condText): ?
                 vlist = []
                 if condText[0] == "`" and condText[-1] == "`":
diff --git a/gui/wxpython/gmodeler/model_convert.py b/gui/wxpython/gmodeler/model_convert.py
index ab9f6885eb2..07735a1b0ee 100644
--- a/gui/wxpython/gmodeler/model_convert.py
+++ b/gui/wxpython/gmodeler/model_convert.py
@@ -56,7 +56,8 @@ def _writeItem(self, item, ignoreBlock=True, variables={}):
             # substitute condition
             cond = item.GetLabel()
             for variable in self.model.GetVariables():
-                pattern = re.compile("%{" + variable + "}")
+                # curly braces are optional
+                pattern = re.compile(r"%(?:\{" + variable + r"\}|" + variable + r")")
                 if pattern.search(cond):
                     value = variables[variable].get("value", "")
                     if variables[variable].get("type", "string") == "string":
@@ -969,14 +970,15 @@ def _substitutePythonParamValue(
             # check for variables
             formattedVar = False
             for var in variables["vars"]:
-                pattern = re.compile("%{" + var + "}")
-                found = pattern.search(value)
+                # curly braces are optional
+                pattern = re.compile(r"%(?:\{" + var + r"\}|" + var + r")")
+                found = pattern.search(parameterizedValue)
                 if found:
                     foundVar = True
                     if found.end() != len(value):
                         formattedVar = True
                         parameterizedValue = pattern.sub(
-                            "{options['" + var + "']}", value
+                            "{options['" + var + "']}", parameterizedValue
                         )
                     else:
                         parameterizedValue = f'options["{var}"]'
diff --git a/gui/wxpython/gmodeler/model_items.py b/gui/wxpython/gmodeler/model_items.py
index c866817ea55..19d8319c944 100644
--- a/gui/wxpython/gmodeler/model_items.py
+++ b/gui/wxpython/gmodeler/model_items.py
@@ -347,7 +347,8 @@ def GetLog(self, string=True, substitute=None):
 
             # order variables by length
             for variable in sorted(variables, key=len, reverse=True):
-                pattern = re.compile("%{" + variable + "}")
+                # curly braces are optional
+                pattern = re.compile(r"%(?:\{" + variable + r"\}|" + variable + r")")
                 value = ""
                 if substitute and "variables" in substitute:
                     for p in substitute["variables"]["params"]: