diff --git a/preprocessor/preprocessor/utilities.py b/preprocessor/preprocessor/utilities.py
index 9160b3c4..1a9af114 100644
--- a/preprocessor/preprocessor/utilities.py
+++ b/preprocessor/preprocessor/utilities.py
@@ -320,9 +320,19 @@ def _check_for_gvcf(in_f) -> bool:
         else:
             line = line.rstrip('\n')
             fields: List[str] = line.split('\t')
-            # check whether input is a block gVCF
-            if re.search('END', fields[7]):
-                return True
+            v_len: int = abs(len(fields[4]) - len(fields[3]))
+            v_start: int = int(fields[1])
+            end_in_info = re.search(r"[;|]?END=(\d+)", fields[7])
+            if end_in_info:
+                end_pos: int = int(end_in_info.group(1))
+                # calculate the length of the variant block indicated by the END annotation in the INFO column
+                end_block = end_pos - v_start
+                if end_block > v_len:
+                    return True
+                elif end_block == v_len:  # not a gVCF if an END block simply annotates the variant length
+                    return False
+                else:  # when end_len < v_len, it is unclear what END annotation stands for
+                    return False
     return False
 
 
diff --git a/preprocessor/tests/test_gvcf_block.vcf b/preprocessor/tests/test_gvcf_block.vcf
new file mode 100644
index 00000000..8315a3f7
--- /dev/null
+++ b/preprocessor/tests/test_gvcf_block.vcf
@@ -0,0 +1,8 @@
+##fileformat=VCFv4.1
+##source=PharmCAT allele definitions
+##reference=hg38
+##contig=<ID=chr11,assembly=hg38,species="Homo sapiens">
+##FILTER=<ID=PASS,Description="All filters passed">
+##FORMAT=<ID=GT,Number=1,Type=String,Description="Genotype">
+#CHROM	POS	ID	REF	ALT	QUAL	FILTER	INFO	FORMAT	Sample_1
+chr1	123456	.	G	A	.	PASS	END=223456	GT	0|0
diff --git a/preprocessor/tests/test_not_gvcf_block.vcf b/preprocessor/tests/test_not_gvcf_block.vcf
new file mode 100644
index 00000000..8f439114
--- /dev/null
+++ b/preprocessor/tests/test_not_gvcf_block.vcf
@@ -0,0 +1,9 @@
+##fileformat=VCFv4.1
+##source=PharmCAT allele definitions
+##reference=hg38
+##contig=<ID=chr11,assembly=hg38,species="Homo sapiens">
+##FILTER=<ID=PASS,Description="All filters passed">
+##FORMAT=<ID=GT,Number=1,Type=String,Description="Genotype">
+#CHROM	POS	ID	REF	ALT	QUAL	FILTER	INFO	FORMAT	Sample_1
+chr1	123456	.	A	T	.	PASS	P|ABEND5|ABEND5	GT	0|1
+chr1	123456	.	GGT	G	.	PASS	END=123458;annotation_of_variant_ending_position	GT	0|1
diff --git a/preprocessor/tests/test_utilities.py b/preprocessor/tests/test_utilities.py
index 4d171219..e1d1d132 100644
--- a/preprocessor/tests/test_utilities.py
+++ b/preprocessor/tests/test_utilities.py
@@ -160,8 +160,14 @@ def test_is_vcf_file():
 def test_is_gvcf_file():
     test_vcf_file = helpers.test_dir / 'raw.vcf.bgz'
     test_gvcf_file = helpers.test_dir / 'test.g.vcf.bgz'
+    test_vcf_end_file = helpers.test_dir / 'test_not_gvcf_block.vcf'
+    test_gvcf_end_file = helpers.test_dir / 'test_gvcf_block.vcf'
     with tempfile.TemporaryDirectory() as td:
         assert not utils.is_gvcf_file(test_vcf_file)
+        # is gVCF as the END annotation indicates a large genomic block
+        assert utils.is_gvcf_file(test_gvcf_end_file)
+        # is not gVCF as the END annotation simply indicates the variant length
+        assert not utils.is_gvcf_file(test_vcf_end_file)
 
         tmp_dir = Path(td)
         f1 = tmp_dir / 'test.g.vcf.bgz'