diff --git a/.gitignore b/.gitignore
index df4e3266d..8e5bd7294 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,6 +6,7 @@ crashes/
 *.pyo
 # Ignore callgrind files
 callgrind.out.*
+gmon.out
 # .hpp files are automatically generated
 *.hpp
 .env
diff --git a/gmon.out b/gmon.out
deleted file mode 100644
index cba10a19b..000000000
Binary files a/gmon.out and /dev/null differ
diff --git a/src/ast/rewriter/seq_subset.cpp b/src/ast/rewriter/seq_subset.cpp
index 2fc4d1f71..f12bc32b1 100644
--- a/src/ast/rewriter/seq_subset.cpp
+++ b/src/ast/rewriter/seq_subset.cpp
@@ -19,7 +19,7 @@ Author:
 
 bool seq_subset::is_subset_rec(expr* a, expr* b, unsigned depth) const {
     while (true) {
-        
+
         if (a == b)
             return true;
         if (m_re.is_empty(a))
@@ -30,7 +30,7 @@ bool seq_subset::is_subset_rec(expr* a, expr* b, unsigned depth) const {
             return true;
 
         if (depth >= m_max_depth)
-            return false;        
+            return false;
 
         expr* a1 = nullptr, * a2 = nullptr, * b1 = nullptr, * b2 = nullptr;
         unsigned la, ua, lb, ub;
@@ -39,16 +39,12 @@ bool seq_subset::is_subset_rec(expr* a, expr* b, unsigned depth) const {
         if (m_re.is_dot_plus(b) && m_re.get_info(a).nullable == l_false)
             return true;
 
-        // a ⊆ a*
-        if (m_re.is_star(b, b1) && is_subset_rec(a, b1, depth))
-            return true;
-
         // e ⊆ a*
         if (m_re.is_epsilon(a) && m_re.is_star(b, b1))
             return true;
 
-        // R ⊆ R*
-        if (m_re.is_star(b, b1) && is_subset_rec(a, b1, depth + 1))
+        // a ⊆ a*: if b = b1* and a ⊆ b1, then a ⊆ b1*
+        if (m_re.is_star(b, b1) && is_subset_rec(a, b1, depth))
             return true;
 
         // R1* ⊆ R2* if R1 ⊆ R2