diff --git a/lib/Infer/Pruning.cpp b/lib/Infer/Pruning.cpp
index b5e55ff7c..ba560cc39 100644
--- a/lib/Infer/Pruning.cpp
+++ b/lib/Infer/Pruning.cpp
@@ -414,7 +414,12 @@ bool PruningManager::isInfeasible(souper::Inst *RHS,
         } else {
           auto RHSV = ConcreteInterpreters[I].evaluateInst(RHS);
           if (RHSV.hasValue()) {
-            if (Val != RHSV.getValue()) {
+            auto RVal = RHSV.getValue();
+            if (SC.LHS->DemandedBits != 0) {
+              Val &= SC.LHS->DemandedBits;
+              RVal &= SC.LHS->DemandedBits;
+            }
+            if (Val != RVal) {
               if (StatsLevel > 2) {
                 llvm::errs() << "  RHS value = " << RHSV.getValue() << "\n";
                 llvm::errs() << "  pruned using concrete interpreter!\n";
diff --git a/test/Infer/pruning/dontprune.opt b/test/Infer/pruning/dontprune.opt
new file mode 100644
index 000000000..c2010064f
--- /dev/null
+++ b/test/Infer/pruning/dontprune.opt
@@ -0,0 +1,18 @@
+; REQUIRES: synthesis
+
+; RUN: %souper-check -try-dataflow-pruning %s > %t
+; RUN: %FileCheck %s < %t
+
+; CHECK: Pruning failed
+
+%0 = block 2
+%1:i64 = var
+%2:i64 = lshr %1, 16:i64
+%3:i64 = var
+%4:i64 = lshr %3, 16:i64
+%5:i64 = phi %0, %2, %4
+%6:i16 = trunc %5
+%7:i32 = zext %6
+infer %7 (demandedBits=00000000000000001111111100000000)
+%8:i32 = trunc %5
+result %8