diff --git a/workflow/rules/common.smk b/workflow/rules/common.smk
index 2bb7d659c..6df89dee4 100644
--- a/workflow/rules/common.smk
+++ b/workflow/rules/common.smk
@@ -166,7 +166,7 @@ def get_read_group(wildcards):
     """Denote sample name and platform in read group."""
     return r"-R '@RG\tID:{sample}\tSM:{sample}\tPL:{platform}'".format(
         sample=wildcards.sample,
-        platform=samples.loc[wildcards.sample, "platform"])
+        platform=samples.loc[[wildcards.sample], "platform"].head(1).item())
 
 
 def get_tmb_targets():