diff --git a/small_RNA-seq/small_RNA-seq.snakefile b/small_RNA-seq/small_RNA-seq.snakefile
index aad860eab8a004abaa912f397065f10932c23707..65b698120e6ff3db162efe748701db3128b808d2 100644
--- a/small_RNA-seq/small_RNA-seq.snakefile
+++ b/small_RNA-seq/small_RNA-seq.snakefile
@@ -4344,6 +4344,9 @@ def source_fold_data(wildcards):
     # 08/06/2023: Take into account new "_by_{norm}" file name element in RPM files
     # possibly set wildcard constraints
     elif fold_type in RPM_FOLD_TYPES:
+        assert wildcards.fold_type.startswith("mean_log2_RPM_by_")
+        assert wildcards.fold_type.endswith("_fold")
+        wildcards.norm = wildcards.fold_type[len("mean_log2_RPM_by_"):-len("_fold")]
         if hasattr(wildcards, "contrast_type"):
             # We want all contrasts of this type.
             #https://stackoverflow.com/a/26791923/1878788