diff --git a/lib/spack/spack/solver/asp.py b/lib/spack/spack/solver/asp.py
index 92734e9afd5..940aae0a72b 100644
--- a/lib/spack/spack/solver/asp.py
+++ b/lib/spack/spack/solver/asp.py
@@ -3829,8 +3829,16 @@ def execute_explicit_splices(self):
         for splice_set in splice_config:
             target = splice_set["target"]
             replacement = spack.spec.Spec(splice_set["replacement"])
-            assert replacement.abstract_hash
-            replacement.replace_hash()
+
+            if not replacement.abstract_hash:
+                location = getattr(
+                    splice_set["replacement"], "_start_mark", " at unknown line number"
+                )
+                msg = f"Explicit splice replacement '{replacement}' does not include a hash.\n"
+                msg += f"{location}\n\n"
+                msg += "    Splice replacements must be specified by hash"
+                raise InvalidSpliceError(msg)
+
             transitive = splice_set.get("transitive", False)
             splice_triples.append((target, replacement, transitive))
 
@@ -3841,6 +3849,10 @@ def execute_explicit_splices(self):
                 if target in current_spec:
                     # matches root or non-root
                     # e.g. mvapich2%gcc
+
+                    # The first iteration, we need to replace the abstract hash
+                    if not replacement.concrete:
+                        replacement.replace_hash()
                     current_spec = current_spec.splice(replacement, transitive)
             new_key = NodeArgument(id=key.id, pkg=current_spec.name)
             specs[new_key] = current_spec
@@ -4226,3 +4238,7 @@ def __init__(self, provided, conflicts):
         # Add attribute expected of the superclass interface
         self.required = None
         self.constraint_type = None
+
+
+class InvalidSpliceError(spack.error.SpackError):
+    """For cases in which the splice configuration is invalid."""
diff --git a/lib/spack/spack/test/concretize.py b/lib/spack/spack/test/concretize.py
index b56f05b6019..553d8fd6426 100644
--- a/lib/spack/spack/test/concretize.py
+++ b/lib/spack/spack/test/concretize.py
@@ -2306,6 +2306,30 @@ def test_explicit_splices(
         assert "hdf5 ^zmpi" in captured.err
         assert str(spec) in captured.err
 
+    def test_explicit_splice_fails_nonexistent(mutable_config, mock_packages, mock_store):
+        splice_info = {"target": "mpi", "replacement": "mpich/doesnotexist"}
+        spack.config.CONFIG.set("concretizer", {"splice": {"explicit": [splice_info]}})
+
+        with pytest.raises(spack.spec.InvalidHashError):
+            _ = spack.spec.Spec("hdf5^zmpi").concretized()
+
+    def test_explicit_splice_fails_no_hash(mutable_config, mock_packages, mock_store):
+        splice_info = {"target": "mpi", "replacement": "mpich"}
+        spack.config.CONFIG.set("concretizer", {"splice": {"explicit": [splice_info]}})
+
+        with pytest.raises(spack.solver.asp.InvalidSpliceError, match="must be specified by hash"):
+            _ = spack.spec.Spec("hdf5^zmpi").concretized()
+
+    def test_explicit_splice_non_match_nonexistent_succeeds(
+        mutable_config, mock_packages, mock_store
+    ):
+        """When we have a nonexistent splice configured but are not using it, don't fail."""
+        splice_info = {"target": "will_not_match", "replacement": "nonexistent/doesnotexist"}
+        spack.config.CONFIG.set("concretizer", {"splice": {"explicit": [splice_info]}})
+        spec = spack.spec.Spec("zlib").concretized()
+        # the main test is that it does not raise
+        assert not spec.spliced
+
     @pytest.mark.db
     @pytest.mark.parametrize(
         "spec_str,mpi_name",