diff --git a/lib/Support/APInt.cpp b/lib/Support/APInt.cpp
index 1cabe0f03e7..8ac589c865f 100644
--- a/lib/Support/APInt.cpp
+++ b/lib/Support/APInt.cpp
@@ -1918,9 +1918,9 @@ void APInt::fromString(unsigned numbits, const char *str, unsigned slen,
   if (isNeg)
     str++, slen--;
   assert((slen <= numbits || radix != 2) && "Insufficient bit width");
-  assert((slen*3 <= numbits || radix != 8) && "Insufficient bit width");
-  assert((slen*4 <= numbits || radix != 16) && "Insufficient bit width");
-  assert(((slen*64)/22 <= numbits || radix != 10) && "Insufficient bit width");
+  assert(((slen-1)*3 <= numbits || radix != 8) && "Insufficient bit width");
+  assert(((slen-1)*4 <= numbits || radix != 16) && "Insufficient bit width");
+  assert((((slen-1)*64)/22 <= numbits || radix != 10) && "Insufficient bit width");
 
   // Allocate memory
   if (!isSingleWord())
@@ -1961,10 +1961,12 @@ void APInt::fromString(unsigned numbits, const char *str, unsigned slen,
     }
 
     // Shift or multiply the value by the radix
-    if (shift)
-      *this <<= shift;
-    else
-      *this *= apradix;
+    if (slen > 1) {
+      if (shift)
+        *this <<= shift;
+      else
+        *this *= apradix;
+    }
 
     // Add in the digit we just interpreted
     if (apdigit.isSingleWord())
diff --git a/unittests/ADT/APIntTest.cpp b/unittests/ADT/APIntTest.cpp
index dcafae2fee8..8ff7d1d8099 100644
--- a/unittests/ADT/APIntTest.cpp
+++ b/unittests/ADT/APIntTest.cpp
@@ -176,4 +176,13 @@ TEST(APIntTest, i1) {
   EXPECT_EQ(zero, one.srem(neg_one));
 }
 
+TEST(APIntTest, fromString) {
+  EXPECT_EQ(APInt(1, 0), APInt(1, "0", 1, 10));
+  EXPECT_EQ(APInt(1, 1), APInt(1, "1", 1, 10));
+  EXPECT_EQ(APInt(1, 1), APInt(1, "-1", 2, 10));
+  EXPECT_EQ(APInt(1, 1), APInt(1, "1", 1, 2));
+  EXPECT_EQ(APInt(1, 1), APInt(1, "1", 1, 8));
+  EXPECT_EQ(APInt(1, 1), APInt(1, "1", 1, 16));
+}
+
 }