diff --git a/include/spdlog/details/circular_q.h b/include/spdlog/details/circular_q.h
index d40e1418..e4fd5fd4 100644
--- a/include/spdlog/details/circular_q.h
+++ b/include/spdlog/details/circular_q.h
@@ -82,7 +82,7 @@ public:
         }
         else
         {
-            return max_items_ - 1 - (head_ - tail_);
+            return max_items_ - (head_ - tail_);
         }
     }
 
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 176578ad..1480b842 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -44,7 +44,9 @@ set(SPDLOG_UTESTS_SOURCES
     test_custom_callbacks.cpp
     test_cfg.cpp
     test_time_point.cpp
-    test_stopwatch.cpp)
+    test_stopwatch.cpp
+    test_circular_q.cpp
+)
 
 if(NOT SPDLOG_NO_EXCEPTIONS)
     list(APPEND SPDLOG_UTESTS_SOURCES test_errors.cpp)
diff --git a/tests/test_circular_q.cpp b/tests/test_circular_q.cpp
new file mode 100644
index 00000000..db5026d9
--- /dev/null
+++ b/tests/test_circular_q.cpp
@@ -0,0 +1,48 @@
+#include "includes.h"
+#include "spdlog/details/circular_q.h"
+
+using q_type = spdlog::details::circular_q<int>;
+TEST_CASE("test_size", "[circular_q]")
+{
+    size_t q_size = 4;
+    q_type q(q_size);
+    REQUIRE(q.size() == 0);
+    REQUIRE(q.empty() == true);
+    for (int i = 0; i < q_size; i++)
+    {
+        q.push_back(std::move(i));
+    }
+    REQUIRE(q.size() == q_size);
+    q.push_back(999);
+    REQUIRE(q.size() == q_size);
+}
+
+TEST_CASE("test_rolling", "[circular_q]")
+{
+    const size_t q_size = 4;
+    q_type q(q_size);
+
+    for (size_t i = 0; i < q_size + 2; i++)
+    {
+        q.push_back(i);
+    }
+
+    REQUIRE(q.size() == q_size);
+
+    REQUIRE(q.front() == 2);
+    q.pop_front();
+
+    REQUIRE(q.front() == 3);
+    q.pop_front();
+
+    REQUIRE(q.front() == 4);
+    q.pop_front();
+
+    REQUIRE(q.front() == 5);
+    q.pop_front();
+
+    REQUIRE(q.empty());
+
+    q.push_back(6);
+    REQUIRE(q.front() == 6);
+}