diff --git a/CHANGELOG.md b/CHANGELOG.md
index b707fdf..65d0971 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,9 @@ adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Fixed
 
+- Explicitly supplied source contents must now cover every source in the
+  receipt; empty and partial mappings report the missing source IDs and fail
+  verification.
 - Verification now reports malformed embedded Ed25519 public keys as a failed
   signature check instead of raising a decoding exception.
 - `verify` and `inspect` now report unreadable or invalid receipt files as
diff --git a/README.md b/README.md
index c570838..ab25e37 100644
--- a/README.md
+++ b/README.md
@@ -143,7 +143,7 @@ Every check is independent and reported separately:
 | ----------- | -------------------------------------------------------------- |
 | `signature` | payload is unmodified and signed by the embedded key           |
 | `merkle`    | recomputed Merkle root matches the signed root                 |
-| `sources`   | supplied source contents hash to the recorded hashes           |
+| `sources`   | every recorded source has supplied content matching its hash   |
 | `grounding` | citations reference real sources; grounding score is honest    |
 | `signer_pin`| (optional) signer public key matches an expected key           |
 
@@ -214,7 +214,7 @@ Merkle forgery vectors.
 answerproof keygen                        # print a keypair as JSON
 answerproof keygen --out id.key           # write id.key and id.key.pub
 answerproof verify receipt.json           # verify (exit 0 = valid, 1 = invalid)
-answerproof verify receipt.json --sources sources.json --json
+answerproof verify receipt.json --sources sources.json --json  # complete source-id mapping
 answerproof verify receipt.json --expect-key <base64>   # pin the signer
 answerproof inspect receipt.json          # human-readable summary
 ```
diff --git a/src/answerproof/verifier.py b/src/answerproof/verifier.py
index 4e4cd27..984d52c 100644
--- a/src/answerproof/verifier.py
+++ b/src/answerproof/verifier.py
@@ -76,7 +76,7 @@ def verify_merkle(receipt: Receipt) -> CheckResult:
 
 
 def verify_sources(receipt: Receipt, contents: dict[str, str]) -> CheckResult:
-    """Check that supplied source contents match their recorded hashes."""
+    """Check that every recorded source has supplied, matching content."""
     by_id = {s.id: s for s in receipt.payload.sources}
     mismatched: list[str] = []
     checked = 0
@@ -88,8 +88,14 @@ def verify_sources(receipt: Receipt, contents: dict[str, str]) -> CheckResult:
         checked += 1
         if not verify_content(content, source.content_hash):
             mismatched.append(sid)
+    missing = [source.id for source in receipt.payload.sources if source.id not in contents]
+    problems: list[str] = []
     if mismatched:
-        return CheckResult("sources", False, "content hash mismatch: " + ", ".join(mismatched))
+        problems.append("content hash mismatch: " + ", ".join(mismatched))
+    if missing:
+        problems.append("missing source content: " + ", ".join(missing))
+    if problems:
+        return CheckResult("sources", False, "; ".join(problems))
     return CheckResult("sources", True, f"{checked} source content(s) matched")
 
 
@@ -151,9 +157,10 @@ def verify_receipt(
 ) -> Verdict:
     """Run all applicable checks and return a :class:`Verdict`.
 
-    ``source_contents`` maps source id -> original content; when supplied the
-    hashes are verified. ``expected_public_key`` pins the signer: if given and
-    it does not match the receipt's key, verification fails.
+    ``source_contents`` maps every source id to its original content; when the
+    mapping is supplied, missing entries and hash mismatches fail verification.
+    ``expected_public_key`` pins the signer: if given and it does not match the
+    receipt's key, verification fails.
     """
     checks: list[CheckResult] = []
     skipped: list[str] = []
@@ -172,7 +179,7 @@ def verify_receipt(
     checks.append(verify_merkle(receipt))
     checks.append(verify_grounding(receipt))
 
-    if source_contents:
+    if source_contents is not None:
         checks.append(verify_sources(receipt, source_contents))
     else:
         skipped.append("sources (no source contents supplied)")
diff --git a/tests/test_verifier.py b/tests/test_verifier.py
index d63858e..0a61ac2 100644
--- a/tests/test_verifier.py
+++ b/tests/test_verifier.py
@@ -18,6 +18,33 @@ def test_verify_without_sources_skips_source_check(receipt):
     assert any("sources" in s for s in verdict.skipped)
 
 
+def test_explicit_empty_source_contents_fails_with_all_missing_ids(receipt):
+    verdict = verify_receipt(receipt, source_contents={})
+
+    assert not verdict.valid
+    source_check = next(c for c in verdict.checks if c.name == "sources")
+    assert not source_check.passed
+    assert source_check.detail == "missing source content: s1, s2, s3"
+
+
+def test_partial_source_contents_fails_with_uncovered_ids(receipt, sources):
+    verdict = verify_receipt(receipt, source_contents={"s1": sources["s1"]})
+
+    assert not verdict.valid
+    source_check = next(c for c in verdict.checks if c.name == "sources")
+    assert not source_check.passed
+    assert source_check.detail == "missing source content: s2, s3"
+
+
+def test_wrong_and_partial_source_contents_report_both_failures(receipt):
+    verdict = verify_receipt(receipt, source_contents={"s1": "wrong"})
+
+    source_check = next(c for c in verdict.checks if c.name == "sources")
+    assert source_check.detail == (
+        "content hash mismatch: s1; missing source content: s2, s3"
+    )
+
+
 def test_signer_pinning_success(receipt, sources):
     pk = receipt.signature.public_key
     verdict = verify_receipt(receipt, source_contents=sources, expected_public_key=pk)