diff --git a/core/base/src/TColorGradient.cxx b/core/base/src/TColorGradient.cxx
index 74c1f4bba761a..2b7a1af7a17bd 100644
--- a/core/base/src/TColorGradient.cxx
+++ b/core/base/src/TColorGradient.cxx
@@ -111,6 +111,9 @@ void TColorGradient::ResetColor(UInt_t nPoints, const Double_t *points,
    fColors.assign(colors, colors + nPoints * 4);
 
    Double_t sum[4] = { 0., 0., 0., 0. };
+   // Clang vectoriser bug. The loop can break with -O2 -mavx2 or similar.
+   // https://github.com/llvm/llvm-project/issues/194008
+#pragma clang loop vectorize(disable)
    for (unsigned n = 0; n < fColors.size(); ++n)
       sum[n % 4] += fColors[n];