diff --git a/image_analysis/indexing/FFTIndexer.cpp b/image_analysis/indexing/FFTIndexer.cpp
index b68d56b8..ecf68998 100644
--- a/image_analysis/indexing/FFTIndexer.cpp
+++ b/image_analysis/indexing/FFTIndexer.cpp
@@ -23,8 +23,8 @@ FFTIndexer::FFTIndexer(const IndexingSettings &settings)
 
     if (max_length_A <= settings.GetFFT_HighResolution_A())
         throw std::invalid_argument("Largest unit cell cannot be smaller than resolution");
-    if (nDirections <= 0)
-        throw std::invalid_argument("FFTWIndexer: number of directions must be > 0");
+    if (nDirections <= 1)
+        throw std::invalid_argument("FFTWIndexer: number of directions must be > 1");
     if (!(max_length_A > 0.f))
         throw std::invalid_argument("FFTWIndexer: max_length_A must be > 0");
     if (!(settings.GetFFT_HighResolution_A() > 0.f))