diff --git a/matlab/olseqs.m b/matlab/olseqs.m
index dc780bac5..283332fad 100644
--- a/matlab/olseqs.m
+++ b/matlab/olseqs.m
@@ -39,13 +39,17 @@ end
 
 jsonmodel = loadjson(jsonfile);
 jsonmodel = jsonmodel.model;
-[lhs, rhs, ~] = getEquationsByTags(jsonmodel, varargin{:});
+[lhs, rhs, lineno] = getEquationsByTags(jsonmodel, varargin{:});
 
 Y = ds{lhs}.data;
 
 rhs_ = strsplit(rhs, {'+','-','*','/','^','log(','exp(','(',')'});
 rhs_(cellfun(@(x) all(isstrprop(x, 'digit')), rhs_)) = [];
 vnames = setdiff(rhs_, cellstr(M_.param_names));
+regexprnoleads = cell2mat(strcat('(', vnames, {'\(\d+\))|'}));
+if ~isempty(regexp(rhs, regexprnoleads(1:end-1), 'match'))
+    error(['olseqs: you cannot have leads in equation on line ' lineno ': ' lhs ' = ' rhs]);
+end
 regexpr = cell2mat(strcat('(', vnames, {'\(-\d+\))|'}));
 vwlags = regexp(rhs, regexpr(1:end-1), 'match');
 X = cell2mat(cellfun(@eval, strcat('ds.', vwlags, '.data'), 'UniformOutput', false));
diff --git a/matlab/plot_contributions.m b/matlab/plot_contributions.m
index 8a673fc0a..5cf42f13e 100644
--- a/matlab/plot_contributions.m
+++ b/matlab/plot_contributions.m
@@ -54,6 +54,11 @@ pnames = cellstr(M_.param_names);
 vnames = setdiff(rhs_, pnames);
 pnames = setdiff(rhs_, vnames);
 
+regexprnoleads = cell2mat(strcat('(', vnames, {'\(\d+\))|'}));
+if ~isempty(regexp(rhs, regexprnoleads(1:end-1), 'match'))
+    error(['plot_contributions: you cannot have leads in equation on line ' lineno ': ' lhs ' = ' rhs]);
+end
+
 % Get values for the parameters
 idp = strmatch(pnames{1}, M_.param_names, 'exact');
 str = sprintf('%s = M_.params(%d);', pnames{1}, idp);