diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6325a6516f..0a62af0ed9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -156,8 +156,8 @@ set(NVIM_API_PRERELEASE true)
 
 # We _want_ assertions in RelWithDebInfo build-type.
 if(CMAKE_C_FLAGS_RELWITHDEBINFO MATCHES DNDEBUG)
-  string(REPLACE "-DNDEBUG" "" CMAKE_C_FLAGS_RELWITHDEBINFO "${CMAKE_C_FLAGS_RELWITHDEBINFO}")
-  string(REPLACE "/DNDEBUG" "" CMAKE_C_FLAGS_RELWITHDEBINFO "${CMAKE_C_FLAGS_RELWITHDEBINFO}")
+  string(REPLACE "-DNDEBUG" "-DRELDEBUG" CMAKE_C_FLAGS_RELWITHDEBINFO "${CMAKE_C_FLAGS_RELWITHDEBINFO}")
+  string(REPLACE "/DNDEBUG" "/DRELDEBUG" CMAKE_C_FLAGS_RELWITHDEBINFO "${CMAKE_C_FLAGS_RELWITHDEBINFO}")
   string(REPLACE "  " " " CMAKE_C_FLAGS_RELWITHDEBINFO "${CMAKE_C_FLAGS_RELWITHDEBINFO}") # Remove duplicate whitespace
 endif()
 
diff --git a/src/nvim/decoration.c b/src/nvim/decoration.c
index 8dbdb7eddc..68ee11d02e 100644
--- a/src/nvim/decoration.c
+++ b/src/nvim/decoration.c
@@ -1068,7 +1068,10 @@ void buf_signcols_count_range(buf_T *buf, int row1, int row2, int add, TriState
     int prevwidth = MIN(SIGN_SHOW_MAX, count[i] - add);
     if (clear != kNone && prevwidth > 0) {
       buf->b_signcols.count[prevwidth - 1]--;
+#ifndef RELDEBUG
+      // TODO(bfredl): correct marktree splicing so that this doesn't fail
       assert(buf->b_signcols.count[prevwidth - 1] >= 0);
+#endif
     }
     int width = MIN(SIGN_SHOW_MAX, count[i]);
     if (clear != kTrue && width > 0) {
diff --git a/src/nvim/marktree.c b/src/nvim/marktree.c
index e2b4296fcd..2902c31f68 100644
--- a/src/nvim/marktree.c
+++ b/src/nvim/marktree.c
@@ -372,7 +372,13 @@ static void unintersect_node(MarkTree *b, MTNode *x, uint64_t id, bool strict)
     }
   }
   if (strict) {
+#ifndef RELDEBUG
+    // TODO(bfredl): This assert has been seen to fail for end users
+    // using RelWithDebInfo builds. While indicating an invalid state for
+    // the marktree, this error doesn't need to be fatal. The assert still
+    // needs to present in Debug builds to be able to detect regressions in tests.
     assert(seen);
+#endif
   }
 
   if (seen) {