diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 2ea6a46..8cc55df 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -10,7 +10,7 @@ stages:
   stage: test
   script:
     - mkdir build && cd build
-    - CXXFLAGS=-Werror cmake -DBUILD_TESTING=1 ..
+    - CXXFLAGS="-Werror -D_GLIBCXX_ASSERTIONS" cmake -DBUILD_TESTING=1 ..
     - make -j$(nproc)
     - broadwayd & CTEST_OUTPUT_ON_FAILURE=1 make test
 
diff --git a/src/tooltips.cpp b/src/tooltips.cpp
index baa604f..30acc68 100644
--- a/src/tooltips.cpp
+++ b/src/tooltips.cpp
@@ -1311,9 +1311,11 @@ void Tooltip::insert_doxygen(const std::string &input_, bool remove_delimiters)
       }
       else {
         auto i2 = i_saved;
-        --i2;
-        while(i2 > 0 && (input[i2] == ' ' || input[i2] == '\t'))
+        if(i2 > 0) {
           --i2;
+          while(i2 > 0 && (input[i2] == ' ' || input[i2] == '\t'))
+            --i2;
+        }
         if(input[i2] == '\n' || i2 == 0)
           markdown += "\n\n";
         if(input[i_saved] == '\\')