diff --git a/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
--- a/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
@@ -183,6 +183,29 @@
                           const Summary &Summary) const override;
   };
 
+  class NotNullConstraint : public ValueConstraint {
+    using ValueConstraint::ValueConstraint;
+    // This variable has a role when we negate the constraint.
+    bool CannotBeNull = true;
+
+  public:
+    ProgramStateRef apply(ProgramStateRef State, const CallEvent &Call,
+                          const Summary &Summary) const override {
+      SVal V = getArgSVal(Call, getArgNo());
+      DefinedOrUnknownSVal L = V.castAs<DefinedOrUnknownSVal>();
+      if (!L.getAs<Loc>())
+        return State;
+
+      return State->assume(L, CannotBeNull);
+    }
+
+    ValueConstraintPtr negate() const override {
+      NotNullConstraint Tmp(*this);
+      Tmp.CannotBeNull = !this->CannotBeNull;
+      return std::make_shared<NotNullConstraint>(Tmp);
+    }
+  };
+
   /// The complete list of constraints that defines a single branch.
   typedef std::vector<ValueConstraintPtr> ConstraintSet;
 
@@ -233,9 +256,6 @@
              "We should have had no significant void types in the spec");
       assert(T.isCanonical() &&
              "We should only have canonical types in the spec");
-      // FIXME: lift this assert (but not the ones above!)
-      assert(T->isIntegralOrEnumerationType() &&
-             "We only support integral ranges in the spec");
     }
 
   public:
@@ -602,6 +622,9 @@
   const QualType LongTy = ACtx.LongTy;
   const QualType LongLongTy = ACtx.LongLongTy;
   const QualType SizeTy = ACtx.getSizeType();
+  const QualType VoidPtrTy = ACtx.VoidPtrTy; // void *T
+  const QualType ConstVoidPtrTy =
+      ACtx.getPointerType(ACtx.VoidTy.withConst()); // const void *T
 
   const RangeInt IntMax = BVF.getMaxValue(IntTy).getLimitedValue();
   const RangeInt LongMax = BVF.getMaxValue(LongTy).getLimitedValue();
@@ -672,6 +695,9 @@
     return IntRangeVector{std::pair<RangeInt, RangeInt>{v, v}};
   };
   auto LessThanOrEq = BO_LE;
+  auto NotNull = [&](ArgNo ArgN) {
+    return std::make_shared<NotNullConstraint>(ArgN);
+  };
 
   using RetType = QualType;
   // Templates for summaries that are reused by many functions.
@@ -687,11 +713,20 @@
                ReturnValueCondition(WithinRange, Range(-1, Max))});
   };
   auto Fread = [&]() {
-    return Summary(ArgTypes{Irrelevant, Irrelevant, SizeTy, Irrelevant},
+    return Summary(ArgTypes{VoidPtrTy, Irrelevant, SizeTy, Irrelevant},
+                   RetType{SizeTy}, NoEvalCall)
+        .Case({
+            ReturnValueCondition(LessThanOrEq, ArgNo(2)),
+        })
+        .ArgConstraint(NotNull(ArgNo(0)));
+  };
+  auto Fwrite = [&]() {
+    return Summary(ArgTypes{ConstVoidPtrTy, Irrelevant, SizeTy, Irrelevant},
                    RetType{SizeTy}, NoEvalCall)
         .Case({
             ReturnValueCondition(LessThanOrEq, ArgNo(2)),
-        });
+        })
+        .ArgConstraint(NotNull(ArgNo(0)));
   };
   auto Getline = [&](RetType R, RangeInt Max) {
     return Summary(ArgTypes{Irrelevant, Irrelevant, Irrelevant}, RetType{R},
@@ -893,7 +928,7 @@
       {"write", Summaries{Read(IntTy, IntMax), Read(LongTy, LongMax),
                           Read(LongLongTy, LongLongMax)}},
       {"fread", Summaries{Fread()}},
-      {"fwrite", Summaries{Fread()}},
+      {"fwrite", Summaries{Fwrite()}},
       // getline()-like functions either fail or read at least the delimiter.
       {"getline", Summaries{Getline(IntTy, IntMax), Getline(LongTy, LongMax),
                             Getline(LongLongTy, LongLongMax)}},
diff --git a/clang/test/Analysis/std-c-library-functions-arg-constraints.c b/clang/test/Analysis/std-c-library-functions-arg-constraints.c
--- a/clang/test/Analysis/std-c-library-functions-arg-constraints.c
+++ b/clang/test/Analysis/std-c-library-functions-arg-constraints.c
@@ -59,3 +59,29 @@
     (void)ret;
   }
 }
+
+typedef struct FILE FILE;
+typedef typeof(sizeof(int)) size_t;
+size_t fread(void *, size_t, size_t, FILE *);
+void test_notnull_concrete(FILE *fp) {
+  fread(0, sizeof(int), 10, fp); // \
+  // report-warning{{Function argument constraint is not satisfied}} \
+  // bugpath-warning{{Function argument constraint is not satisfied}} \
+  // bugpath-note{{Function argument constraint is not satisfied}}
+}
+void test_notnull_symbolic(FILE *fp, int *buf) {
+  fread(buf, sizeof(int), 10, fp);
+  clang_analyzer_eval(buf != 0); // \
+  // report-warning{{TRUE}} \
+  // bugpath-warning{{TRUE}} \
+  // bugpath-note{{TRUE}} \
+  // bugpath-note{{'buf' is not equal to null}}
+}
+void test_notnull_symbolic2(FILE *fp, int *buf) {
+  if (!buf) // bugpath-note{{Assuming 'buf' is null}} \
+            // bugpath-note{{Taking true branch}}
+    fread(buf, sizeof(int), 10, fp); // \
+    // report-warning{{Function argument constraint is not satisfied}} \
+    // bugpath-warning{{Function argument constraint is not satisfied}} \
+    // bugpath-note{{Function argument constraint is not satisfied}}
+}
diff --git a/clang/test/Analysis/std-c-library-functions.c b/clang/test/Analysis/std-c-library-functions.c
--- a/clang/test/Analysis/std-c-library-functions.c
+++ b/clang/test/Analysis/std-c-library-functions.c
@@ -78,10 +78,13 @@
 size_t fread(void *, size_t, size_t, FILE *);
 size_t fwrite(const void *restrict, size_t, size_t, FILE *restrict);
 void test_fread_fwrite(FILE *fp, int *buf) {
+
   size_t x = fwrite(buf, sizeof(int), 10, fp);
   clang_analyzer_eval(x <= 10); // expected-warning{{TRUE}}
+
   size_t y = fread(buf, sizeof(int), 10, fp);
   clang_analyzer_eval(y <= 10); // expected-warning{{TRUE}}
+
   size_t z = fwrite(buf, sizeof(int), y, fp);
   clang_analyzer_eval(z <= y); // expected-warning{{TRUE}}
 }