diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc
index 91dd332a2..34b1342a0 100644
--- a/src/libfetchers/git.cc
+++ b/src/libfetchers/git.cc
@@ -187,8 +187,16 @@ struct GitInputScheme : InputScheme
         if (submodules) cacheType += "-submodules";
         if (allRefs) cacheType += "-all-refs";
 
+        auto checkHashType = [&](const std::optional<Hash> & hash)
+        {
+            if (hash.has_value() && !(hash->type == htSHA1 || hash->type == htSHA256))
+                throw Error("Hash '%s' is not supported by Git. Supported types are sha1 and sha256.", hash->to_string(Base16, true));
+        };
+
         auto getLockedAttrs = [&]()
         {
+            checkHashType(input.getRev());
+
             return Attrs({
                 {"type", cacheType},
                 {"name", name},
diff --git a/src/libfetchers/mercurial.cc b/src/libfetchers/mercurial.cc
index 51cf35bf4..1beb8b944 100644
--- a/src/libfetchers/mercurial.cc
+++ b/src/libfetchers/mercurial.cc
@@ -203,8 +203,17 @@ struct MercurialInputScheme : InputScheme
 
         if (!input.getRef()) input.attrs.insert_or_assign("ref", "default");
 
+        auto checkHashType = [&](const std::optional<Hash> & hash)
+        {
+            if (hash.has_value() && hash->type != htSHA1)
+                throw Error("Hash '%s' is not supported by Mercurial. Only sha1 is supported.", hash->to_string(Base16, true));
+        };
+
+
         auto getLockedAttrs = [&]()
         {
+            checkHashType(input.getRev());
+
             return Attrs({
                 {"type", "hg"},
                 {"name", name},