diff --git a/mlir/lib/Dialect/SCF/SCF.cpp b/mlir/lib/Dialect/SCF/SCF.cpp
--- a/mlir/lib/Dialect/SCF/SCF.cpp
+++ b/mlir/lib/Dialect/SCF/SCF.cpp
@@ -1768,6 +1768,10 @@
     if (op.elseBlock())
       llvm::append_range(elseYield, op.elseYield().getOperands());
 
+    // A list of indices for which we should upgrade the value yielded
+    // in the else to a select.
+    SmallVector<unsigned> elseYieldsToUpgradeToSelect;
+
     // If the outer scf.if yields a value produced by the inner scf.if,
     // only permit combining if the value yielded when the condition
     // is false in the outer scf.if is the same value yielded when the
@@ -1785,6 +1789,22 @@
         // If the correctness test passes, we will yield
         // corresponding value from the inner scf.if
         thenYield[tup.index()] = nestedIf.thenYield().getOperand(nestedIdx);
+        continue;
+      }
+
+      // Otherwise, we need to ensure the else block of the combined
+      // condition still returns the same value when the outer condition is
+      // true and the inner condition is false. This can be accomplished if
+      // the then value is defined outside the outer scf.if and we replace the
+      // value with a select that considers just the outer condition. Since
+      // the else region contains just the yield, its yielded value is
+      // defined outside the scf.if, by definition.
+
+      // If the then value is defined within the scf.if, bail.
+      if (tup.value().getParentRegion() == &op.getThenRegion()) {
+        return failure();
+      } else {
+        elseYieldsToUpgradeToSelect.push_back(tup.index());
       }
     }
 
@@ -1792,6 +1812,15 @@
     Value newCondition = rewriter.create<arith::AndIOp>(
         loc, op.getCondition(), nestedIf.getCondition());
     auto newIf = rewriter.create<IfOp>(loc, op.getResultTypes(), newCondition);
+
+    SmallVector<Value> results;
+    llvm::append_range(results, newIf.getResults());
+    rewriter.setInsertionPoint(newIf);
+
+    for (auto idx : elseYieldsToUpgradeToSelect)
+      results[idx] = rewriter.create<arith::SelectOp>(
+          op.getLoc(), op.getCondition(), thenYield[idx], elseYield[idx]);
+
     Block *newIfBlock = newIf.thenBlock();
     if (newIfBlock)
       rewriter.eraseOp(newIfBlock->getTerminator());
@@ -1805,7 +1834,7 @@
       rewriter.setInsertionPointToEnd(newIf.elseBlock());
       rewriter.create<YieldOp>(loc, elseYield);
     }
-    rewriter.replaceOp(op, newIf.getResults());
+    rewriter.replaceOp(op, results);
     return success();
   }
 };
diff --git a/mlir/test/Dialect/SCF/canonicalize.mlir b/mlir/test/Dialect/SCF/canonicalize.mlir
--- a/mlir/test/Dialect/SCF/canonicalize.mlir
+++ b/mlir/test/Dialect/SCF/canonicalize.mlir
@@ -556,7 +556,7 @@
 // CHECK: %[[PRE0:.*]] = "test.op"() : () -> i32
 // CHECK: %[[PRE1:.*]] = "test.op1"() : () -> i32
 // CHECK: %[[COND:.*]] = arith.andi %[[ARG0]], %[[ARG1]]
-// CHECK: %[[RES:.*]] = arith.select %[[COND]], %[[PRE0]], %[[PRE1]]
+// CHECK: %[[RES:.*]] = arith.select %[[ARG0]], %[[PRE0]], %[[PRE1]]
 // CHECK: scf.if %[[COND]] 
 // CHECK:   "test.run"() : () -> ()
 // CHECK: }
@@ -596,6 +596,7 @@
   }
   return %r#0, %r#1, %r#2, %r#3 : i32, f32, i32, i8
 }
+
 // -----
 
 // CHECK-LABEL:   func @if_condition_swap