diff --git a/Tests/DeterminismDifferentialTests.swift b/Tests/DeterminismDifferentialTests.swift
index 2d6c1f9..3d51c1b 100644
--- a/Tests/DeterminismDifferentialTests.swift
+++ b/Tests/DeterminismDifferentialTests.swift
@@ -87,7 +87,8 @@ struct DeterminismDifferentialTests {
     @Test("PureXML's UPA verdict agrees with libxml2 over generated content models")
     func test_determinismDifferential() {
         guard enabled, let xmllint else { return }
-        var generator = DeterminismSchemaGenerator(seed: 0xDE7E_5A11_C0DE_F00D)
+        let seed = ProcessInfo.processInfo.environment["DIFF_SEED"].flatMap { UInt64($0) } ?? 0xDE7E_5A11_C0DE_F00D
+        var generator = DeterminismSchemaGenerator(seed: seed)
         var falsePositives: [String] = []
         var falseNegatives: [String] = []
         var compared = 0
diff --git a/Tests/FacetValidationDifferentialTests.swift b/Tests/FacetValidationDifferentialTests.swift
index bcedfdd..a52cef7 100644
--- a/Tests/FacetValidationDifferentialTests.swift
+++ b/Tests/FacetValidationDifferentialTests.swift
@@ -114,7 +114,8 @@ struct FacetValidationDifferentialTests {
     @Test("PureXML's facet-validity verdict agrees with libxml2 over generated values")
     func test_facetDifferential() {
         guard enabled, let xmllint else { return }
-        var generator = FacetSchemaGenerator(seed: 0xFACE_7D1F_F00D_C0DE)
+        let seed = ProcessInfo.processInfo.environment["DIFF_SEED"].flatMap { UInt64($0) } ?? 0xFACE_7D1F_F00D_C0DE
+        var generator = FacetSchemaGenerator(seed: seed)
         var tally = Tally()
         let schemaFile = NSTemporaryDirectory() + "facet-diff-schema.xsd"
         for _ in 0 ..< 2000 {
diff --git a/Tests/InstanceValidationDifferentialTests.swift b/Tests/InstanceValidationDifferentialTests.swift
index fe543fb..dee8c6f 100644
--- a/Tests/InstanceValidationDifferentialTests.swift
+++ b/Tests/InstanceValidationDifferentialTests.swift
@@ -107,7 +107,8 @@ struct InstanceValidationDifferentialTests {
     @Test("PureXML's instance-validity verdict agrees with libxml2 over generated documents")
     func test_instanceDifferential() {
         guard enabled, let xmllint else { return }
-        var generator = InstanceSchemaGenerator(seed: 0x1A57_C0DE_5EED_BEEF)
+        let seed = ProcessInfo.processInfo.environment["DIFF_SEED"].flatMap { UInt64($0) } ?? 0x1A57_C0DE_5EED_BEEF
+        var generator = InstanceSchemaGenerator(seed: seed)
         var tally = Tally()
         let schemaFile = NSTemporaryDirectory() + "inst-diff-schema.xsd"
         for _ in 0 ..< 1500 {