diff --git a/interp/interpreter.go b/interp/interpreter.go
index 864d6f65..605f4d8f 100644
--- a/interp/interpreter.go
+++ b/interp/interpreter.go
@@ -644,11 +644,11 @@ func (r *runner) run(fn *function, params []value, parentMem *memoryView, indent
 		case llvm.GetElementPtr:
 			// GetElementPtr does pointer arithmetic, changing the offset of the
 			// pointer into the underlying object.
-			var offset uint64
+			var offset int64
 			for i := 1; i < len(operands); i += 2 {
-				index := operands[i].Uint()
-				elementSize := operands[i+1].Uint()
-				if int64(elementSize) < 0 {
+				index := operands[i].Int()
+				elementSize := operands[i+1].Int()
+				if elementSize < 0 {
 					// This is a struct field.
 					offset += index
 				} else {
@@ -662,7 +662,7 @@ func (r *runner) run(fn *function, params []value, parentMem *memoryView, indent
 					return nil, mem, r.errorAt(inst, err)
 				}
 				// GEP on fixed pointer value (for example, memory-mapped I/O).
-				ptrValue := operands[0].Uint() + offset
+				ptrValue := operands[0].Uint() + uint64(offset)
 				locals[inst.localIndex] = makeLiteralInt(ptrValue, int(operands[0].len(r)*8))
 				continue
 			}
diff --git a/interp/testdata/basic.ll b/interp/testdata/basic.ll
index 6d1d010f..0275dcbb 100644
--- a/interp/testdata/basic.ll
+++ b/interp/testdata/basic.ll
@@ -10,6 +10,8 @@ target triple = "x86_64--linux"
 @main.exposedValue1 = global i16 0
 @main.exposedValue2 = global i16 0
 @main.insertedValue = global {i8, i32, {float, {i64, i16}}} zeroinitializer
+@main.gepArray = global [8 x i8] zeroinitializer
+@main.negativeGEP = global ptr null
 
 declare void @runtime.printint64(i64) unnamed_addr
 
@@ -88,6 +90,11 @@ entry:
   %agg2 = insertvalue {i8, i32, {float, {i64, i16}}} %agg, i64 5, 2, 1, 0
   store {i8, i32, {float, {i64, i16}}} %agg2, ptr @main.insertedValue
 
+  ; negative GEP instruction
+  %ngep1 = getelementptr [8 x i8], ptr @main.negativeGEP, i32 0, i32 5
+  %ngep2 = getelementptr [8 x i8], ptr %ngep1, i32 0, i32 -3
+  store ptr %ngep2, ptr @main.negativeGEP
+
   ret void
 }
 
diff --git a/interp/testdata/basic.out.ll b/interp/testdata/basic.out.ll
index 342d4965..2685850e 100644
--- a/interp/testdata/basic.out.ll
+++ b/interp/testdata/basic.out.ll
@@ -9,6 +9,8 @@ target triple = "x86_64--linux"
 @main.exposedValue1 = global i16 0
 @main.exposedValue2 = local_unnamed_addr global i16 0
 @main.insertedValue = local_unnamed_addr global { i8, i32, { float, { i64, i16 } } } zeroinitializer
+@main.gepArray = local_unnamed_addr global [8 x i8] zeroinitializer
+@main.negativeGEP = global ptr getelementptr inbounds (i8, ptr @main.negativeGEP, i64 2)
 
 declare void @runtime.printint64(i64) unnamed_addr