diff --git a/doc/manual/change-authors.yml b/doc/manual/change-authors.yml
index df8f0d006..449ab534c 100644
--- a/doc/manual/change-authors.yml
+++ b/doc/manual/change-authors.yml
@@ -133,6 +133,11 @@ roberth:
   display_name: Robert Hensing
   github: roberth
 
+tcmal:
+  display_name: Aria
+  forgejo: tcmal
+  github: tcmal
+
 thufschmitt:
   display_name: Théophane Hufschmitt
   github: thufschmitt
diff --git a/doc/manual/rl-next/reject-weak-hashes.md b/doc/manual/rl-next/reject-weak-hashes.md
new file mode 100644
index 000000000..4b027a368
--- /dev/null
+++ b/doc/manual/rl-next/reject-weak-hashes.md
@@ -0,0 +1,11 @@
+---
+synopsis: "Weak hash algorithms are now rejected in SRI form, and cause a warning otherwise"
+category: Breaking Changes
+credits: tcmal
+cls: [2110]
+issues: [8982, fj#114]
+---
+
+MD5 and SHA-1 algorithms are now no longer allowed in SRI form, as specified in [the spec](https://w3c.github.io/webappsec-subresource-integrity/#hash-functions).
+
+These hash types will also give a warning when used in other cases.
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index d383e9802..280b815d2 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -8,6 +8,7 @@
 #include "hash.hh"
 #include "archive.hh"
 #include "charptr-cast.hh"
+#include "fmt.hh"
 #include "logging.hh"
 #include "split.hh"
 #include "strings.hh"
@@ -210,6 +211,17 @@ Hash Hash::parseNonSRIUnprefixed(std::string_view s, HashType type)
 Hash::Hash(std::string_view rest, HashType type, bool isSRI)
     : Hash(type)
 {
+    if (type == HashType::MD5 || type == HashType::SHA1) {
+        if (isSRI) {
+            // Forbidden as per https://w3c.github.io/webappsec-csp/#grammardef-hash-algorithm
+            throw BadHash("%s values are not allowed in SRI hashes", printHashType(type));
+        } else {
+            logWarning({
+                    .msg = HintFmt("%s hashes are considered weak, use a newer hashing algorithm instead. (value: %s)", Uncolored(printHashType(type)), rest)
+            });
+        }
+    }
+
     if (!isSRI && rest.size() == base16Len()) {
 
         auto parseHexDigit = [&](char c) {
diff --git a/tests/functional/hash.sh b/tests/functional/hash.sh
index 34c1bb38a..aeebf298d 100644
--- a/tests/functional/hash.sh
+++ b/tests/functional/hash.sh
@@ -102,6 +102,5 @@ try3() {
     h16=$(nix hash to-base16 "$sri")
     [ "$h16" = "$2" ]
 }
-try3 sha1 "800d59cfcd3c05e900cb4e214be48f6b886a08df" "vw46m23bizj4n8afrc0fj19wrp7mj3c0" "gA1Zz808BekAy04hS+SPa4hqCN8="
 try3 sha256 "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad" "1b8m03r63zqhnjf7l5wnldhh7c134ap5vpj0850ymkq1iyzicy5s" "ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0="
 try3 sha512 "204a8fc6dda82f0a0ced7beb8e08a41657c16ef468b228a8279be331a703c33596fd15c13b1b07f9aa1d3bea57789ca031ad85c7a71dd70354ec631238ca3445" "12k9jiq29iyqm03swfsgiw5mlqs173qazm3n7daz43infy12pyrcdf30fkk3qwv4yl2ick8yipc2mqnlh48xsvvxl60lbx8vp38yji0" "IEqPxt2oLwoM7XvrjgikFlfBbvRosiioJ5vjMacDwzWW/RXBOxsH+aodO+pXeJygMa2Fx6cd1wNU7GMSOMo0RQ=="
diff --git a/tests/functional/meson.build b/tests/functional/meson.build
index 891a755d7..03eadc570 100644
--- a/tests/functional/meson.build
+++ b/tests/functional/meson.build
@@ -197,6 +197,7 @@ functional_tests_scripts = [
   'extra-sandbox-profile.sh',
   'substitute-truncated-nar.sh',
   'regression-484.sh',
+  'reject-weak-hashes.sh'
 ]
 
 # Plugin tests require shared libraries support.
diff --git a/tests/functional/reject-weak-hashes.sh b/tests/functional/reject-weak-hashes.sh
new file mode 100644
index 000000000..3565604f1
--- /dev/null
+++ b/tests/functional/reject-weak-hashes.sh
@@ -0,0 +1,11 @@
+source common.sh
+
+expectStderr 1 nix hash to-sri md5-rrdBU2a35b2PM2ZO+n/zGw== \
+  | grepQuiet "md5 values are not allowed"
+expectStderr 1 nix hash to-sri sha1-SXZKz6Po0xFryhnhSDvvOfAuBOo= \
+  | grepQuiet "sha1 values are not allowed"
+
+nix hash to-sri --type md5 a180c3fe91680389c210c99def54d9e0 2>&1 \
+  | grepQuiet "md5 hashes are considered weak"
+nix hash to-sri --type sha1 49764acfa3e8d3116bca19e1483bef39f02e04ea 2>&1 \
+  | grepQuiet "sha1 hashes are considered weak"