diff --git a/common/source/java/ch/systemsx/cisd/common/fasta/FastaUtilities.java b/common/source/java/ch/systemsx/cisd/common/fasta/FastaUtilities.java
index 6d79e381033775f35c78b760dd146ca2f46c1bc2..99faa80f4a56405c014221ca1712b81e9ffbb305 100644
--- a/common/source/java/ch/systemsx/cisd/common/fasta/FastaUtilities.java
+++ b/common/source/java/ch/systemsx/cisd/common/fasta/FastaUtilities.java
@@ -61,7 +61,7 @@ public class FastaUtilities
             boolean isAmoniAcidCode = AMINO_ACID_CODES_SET.contains(c);
             if (isNucleicAcidCode == false && isAmoniAcidCode == false)
             {
-                throw new IllegalArgumentException("Invalid symbol '" + c + "' in line '" + line + "'.");
+                continue;
             }
             if (isNucleicAcidCode == false)
             {