diff --git a/include/tags/context.hpp b/include/tags/context.hpp
index 424ee9d0..21d6a628 100644
--- a/include/tags/context.hpp
+++ b/include/tags/context.hpp
@@ -158,8 +158,8 @@ namespace tags {
     bool has_double_click() const;
 
     size_t num_actions() const;
+    size_t num_unclosed() const;
 
-    // TODO provide better interface for adjusting the start positions of actions
     const std::vector<action_block>& get_blocks() const;
 
    protected:
diff --git a/src/tags/context.cpp b/src/tags/context.cpp
index ec0873e3..c3046a86 100644
--- a/src/tags/context.cpp
+++ b/src/tags/context.cpp
@@ -198,6 +198,18 @@ namespace tags {
     return m_action_blocks.size();
   }
 
+  size_t action_context::num_unclosed() const {
+    size_t num = 0;
+
+    for (const auto& a : m_action_blocks) {
+      if (a.is_open) {
+        num++;
+      }
+    }
+
+    return num;
+  }
+
   const std::vector<action_block>& action_context::get_blocks() const {
     return m_action_blocks;
   }
diff --git a/src/tags/dispatch.cpp b/src/tags/dispatch.cpp
index 222df632..66c49ae4 100644
--- a/src/tags/dispatch.cpp
+++ b/src/tags/dispatch.cpp
@@ -100,14 +100,19 @@ namespace tags {
       }
     }
 
+    /*
+     * After rendering, we need to tell the action context about the position
+     * of the alignment blocks so that it can do intersection tests.
+     */
     for (auto a : {alignment::LEFT, alignment::CENTER, alignment::RIGHT}) {
       m_action_ctxt.set_alignmnent_start(a, renderer.get_alignment_start(a));
     }
 
-    // TODO handle unclosed action tags in ctxt
-    /* if (!m_actions.empty()) { */
-    /*   throw runtime_error(to_string(m_actions.size()) + " unclosed action block(s)"); */
-    /* } */
+    auto num_unclosed = m_action_ctxt.num_unclosed();
+
+    if (num_unclosed != 0) {
+      throw runtime_error(to_string(num_unclosed) + " unclosed action block(s)");
+    }
   }
 
   /**
diff --git a/tests/unit_tests/tags/action_context.cpp b/tests/unit_tests/tags/action_context.cpp
index a5be8414..7d1bec34 100644
--- a/tests/unit_tests/tags/action_context.cpp
+++ b/tests/unit_tests/tags/action_context.cpp
@@ -46,6 +46,7 @@ TEST(ActionCtxtTest, closing) {
   EXPECT_EQ(make_pair(id2, mousebtn::RIGHT), ctxt.action_close(mousebtn::NONE, alignment::CENTER, 1));
 
   EXPECT_EQ(4, ctxt.num_actions());
+  EXPECT_EQ(0, ctxt.num_unclosed());
 }
 
 TEST(ActionCtxtTest, overlapping) {
@@ -76,6 +77,7 @@ TEST(ActionCtxtTest, overlapping) {
   EXPECT_EQ(id3, actions[mousebtn::RIGHT]);
 
   EXPECT_EQ(3, ctxt.num_actions());
+  EXPECT_EQ(0, ctxt.num_unclosed());
 }
 
 TEST(ActionCtxtTest, stacking) {
@@ -109,6 +111,7 @@ TEST(ActionCtxtTest, stacking) {
   EXPECT_EQ(id1, ctxt.has_action(mousebtn::LEFT, 7));
 
   EXPECT_EQ(3, ctxt.num_actions());
+  EXPECT_EQ(0, ctxt.num_unclosed());
 }
 
 TEST(ActionCtxtTest, cmd) {