diff --git a/src/material.cc b/src/material.cc
index 74405274da..601addf35a 100644
--- a/src/material.cc
+++ b/src/material.cc
@@ -106,8 +106,8 @@ void Material::Absorb(Material::Ptr mat) {
 
   // force both mateiral objects to advance to the same decay time
   int common_decay_time = std::max(this->prev_decay_time_, mat->prev_decay_time_);
-  if (ctx_ != NULL && ctx_->sim_info().decay != "never") {
-    common_decay_time = ctx_->time();    
+  if (HasContext() && mat->HasContext() && ctx_->sim_info().decay != "never") {
+    common_decay_time = std::max(ctx_->time(), common_decay_time);    
   }
   mat->Decay(common_decay_time);
   this->Decay(common_decay_time);
@@ -128,7 +128,11 @@ void Material::Absorb(Material::Ptr mat) {
     comp_ = Composition::CreateFromMass(compmath::Add(v, otherv));
   }
   
-  qty_ += mat->qty_;
+  double tot_mass = qty_ + mat->quantity();
+  double avg_unit_value =
+      (qty_ * UnitValue() + mat->quantity() * mat->UnitValue()) / tot_mass;
+  SetUnitValue(avg_unit_value);
+  qty_ = tot_mass;
   mat->qty_ = 0;
   tracker_.Absorb(&mat->tracker_);
 }
@@ -204,7 +208,8 @@ void Material::Decay(int curr_time) {
     curr_time = ctx_->time();
   }
 
-  int dt = curr_time - prev_decay_time_;
+  // Block backwards decay with std::max
+  int dt = std::max(curr_time - prev_decay_time_, 0);
   if (dt == 0) {
     return;
   }
@@ -242,7 +247,8 @@ void Material::Decay(int curr_time) {
     }
   }
 
-  prev_decay_time_ = curr_time;  // this must go before Transmute call
+  // Need to set prev_decay_time before Transmute. Block setting it backwards.
+  prev_decay_time_ = std::max(curr_time, prev_decay_time_); 
   Composition::Ptr decayed = comp_->Decay(dt, secs_per_timestep);
   Transmute(decayed);
 }
diff --git a/src/material.h b/src/material.h
index 9ed29950b4..2e7635069a 100644
--- a/src/material.h
+++ b/src/material.h
@@ -108,6 +108,9 @@ class Material : public Resource {
   /// Returns the mass of this material in kg.
   virtual double quantity() const;
 
+  /// Returns true if the material has a context, false otherwise.
+  virtual bool HasContext() const {return ctx_ != NULL;}
+
   virtual Resource::Ptr ExtractRes(double qty);
 
   /// Same as ExtractComp with c = this->comp().
diff --git a/tests/material_tests.cc b/tests/material_tests.cc
index a0566102f8..341c5c0e63 100644
--- a/tests/material_tests.cc
+++ b/tests/material_tests.cc
@@ -134,6 +134,38 @@ TEST_F(MaterialTest, AbsorbIntoZeroMaterial) {
   EXPECT_FLOAT_EQ(test_size_, same_as_test_mat->quantity());
 }
 
+TEST_F(MaterialTest, AbsorbMatlWithoutContext) {
+  Material::Ptr no_ctx_mat = Material::CreateUntracked(0, test_comp_);
+  EXPECT_FALSE(no_ctx_mat->HasContext());
+  EXPECT_NO_THROW(test_mat_->Absorb(no_ctx_mat));
+}
+
+TEST_F(MaterialTest, BackwardsDecay) {
+  FakeContext* fake_ctx = new FakeContext(&ti, &rec);
+  TestFacility* fake_fac = new TestFacility(fake_ctx);
+
+  Material::Ptr m1 = Material::Create(fake_fac, 1, diff_comp_);
+  Material::Ptr m2 = Material::Create(fake_fac, 1, diff_comp_);
+
+  // Set context time to 10 to match the decay time
+  fake_ctx->time(10);
+
+  m2->Decay(); // decay m2 to time 10
+  EXPECT_EQ(0, m1->prev_decay_time());
+  EXPECT_EQ(10, m2->prev_decay_time());
+
+  fake_ctx->time(9);
+
+  // After manually setting the ctx time backwards, common_decay_time is 10,
+  // and ctx->time() is 9, meaning decay will set dt = 0 with std::max, and 
+  // prev_decay_time for the combined mat should remain at 10.
+  m1->Absorb(m2);
+  EXPECT_EQ(10, m1->prev_decay_time());
+
+  delete fake_fac;
+  delete fake_ctx;
+}
+
 TEST_F(MaterialTest, ExtractMass) {
   double amt = test_size_ / 3;
   double diff = test_size_ - amt;
@@ -408,23 +440,34 @@ TEST_F(MaterialTest, TransmutePrevDecay) {
 // as coded.  We may decide to change the behavior in the future breaking
 // this test; the test will need to be modified accordingly.
 //
-// This test checks to see that, when materials are absorbed together, the
-// previous decay time for the larger quantity material is used as the value
-// for the new, combined material.
+// This test checks to see that, when materials are absorbed together, both 
+// materials are decayed prior to the absorption.
+
 TEST_F(MaterialTest, AbsorbPrevDecay) {
-  Material::Ptr m1 = Material::Create(fac, 1, diff_comp_);
-  Material::Ptr m2 = Material::Create(fac, 1, diff_comp_);
-  Material::Ptr m3 = Material::Create(fac, 1000, diff_comp_);
-  m3->Decay(10);
+  FakeContext* fake_ctx = new FakeContext(&ti, &rec);
+  TestFacility* fake_fac = new TestFacility(fake_ctx);
+
+  Material::Ptr m1 = Material::Create(fake_fac, 1, diff_comp_);
+  Material::Ptr m2 = Material::Create(fake_fac, 1, diff_comp_);
+  Material::Ptr m3 = Material::Create(fake_fac, 1000, diff_comp_);
 
+  // Set context time to 10 to match the decay time
+  fake_ctx->time(10);
+
+  m3->Decay(); // decay m3 to time 10
   EXPECT_EQ(0, m1->prev_decay_time());
   EXPECT_EQ(0, m2->prev_decay_time());
   EXPECT_EQ(10, m3->prev_decay_time());
 
+  fake_ctx->time(11);
+
   m1->Absorb(m3);
-  EXPECT_EQ(10, m1->prev_decay_time());
+  EXPECT_EQ(11, m1->prev_decay_time());
   m1->Absorb(m2);
-  EXPECT_EQ(10, m1->prev_decay_time());
+  EXPECT_EQ(11, m1->prev_decay_time());
+
+  delete fake_fac;
+  delete fake_ctx;
 }
 
 TEST_F(MaterialTest, DecayHeatTest) {
diff --git a/tests/material_tests.h b/tests/material_tests.h
index a562f21b3d..e49b4c35f5 100644
--- a/tests/material_tests.h
+++ b/tests/material_tests.h
@@ -11,6 +11,7 @@
 #include "test_agents/test_facility.h"
 #include "recorder.h"
 #include "timer.h"
+#include "test_context.h"
 
 
 namespace cyclus {