diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index 69a1c0c..32a1726 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -386,8 +386,8 @@
       
       // The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale.
       // This gives us an aggregate computation of (C1*Scale)*V + C2*Scale.
-      BaseOffs += IndexOffset.getZExtValue()*Scale;
-      Scale *= IndexScale.getZExtValue();
+      BaseOffs += IndexOffset.getSExtValue()*Scale;
+      Scale *= IndexScale.getSExtValue();
       
       
       // If we already had an occurrance of this index variable, merge this
@@ -407,7 +407,7 @@
       // pointer size.
       if (unsigned ShiftBits = 64-TD->getPointerSizeInBits()) {
         Scale <<= ShiftBits;
-        Scale >>= ShiftBits;
+        Scale = (int64_t)Scale >> ShiftBits;
       }
       
       if (Scale) {
diff --git a/test/Analysis/BasicAA/2010-09-15-GEP-SignedArithmetic.ll b/test/Analysis/BasicAA/2010-09-15-GEP-SignedArithmetic.ll
new file mode 100644
index 0000000..2b0cd78
--- /dev/null
+++ b/test/Analysis/BasicAA/2010-09-15-GEP-SignedArithmetic.ll
@@ -0,0 +1,15 @@
+; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info -disable-output |& grep {1 may alias}
+; PR7959
+
+target datalayout = "e-p:32:32:32"
+
+define i32 @test(i32* %tab, i32 %indvar) nounwind {
+  %tmp31 = mul i32 %indvar, -2
+  %tmp32 = add i32 %tmp31, 30
+  %t.5 = getelementptr i32* %tab, i32 %tmp32
+  %loada = load i32* %tab
+  store i32 0, i32* %t.5
+  %loadb = load i32* %tab
+  %rval = add i32 %loada, %loadb
+  ret i32 %rval
+}