diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -290,6 +290,11 @@
 - Introduced the new function ``clang_CXXMethod_isExplicit``,
   which identifies whether a constructor or conversion function cursor
   was marked with the explicit identifier.
+- Added check in ``clang_getFieldDeclBitWidth`` for whether a bit field
+  has an evaluable bit width. Fixes undefined behavior when called on a
+  bit field whose width depends on a template paramter.
+- Added function ``clang_isFieldDeclBitWidthDependent`` to check if a
+  bit field's width depends on a template parameter.
 
 Static Analyzer
 ---------------
diff --git a/clang/include/clang-c/Index.h b/clang/include/clang-c/Index.h
--- a/clang/include/clang-c/Index.h
+++ b/clang/include/clang-c/Index.h
@@ -2887,10 +2887,19 @@
 CINDEX_LINKAGE unsigned long long
 clang_getEnumConstantDeclUnsignedValue(CXCursor C);
 
+/**
+ * Returns non-zero if a bit field's width depends on template parameters.
+ *
+ * If the cursor does not reference a bit field declaration or if the bit
+ * field's width does not depend on template parameters, 0 is returned.
+ */
+CINDEX_LINKAGE unsigned clang_isFieldDeclBitWidthDependent(CXCursor C);
+
 /**
  * Retrieve the bit width of a bit field declaration as an integer.
  *
- * If a cursor that is not a bit field declaration is passed in, -1 is returned.
+ * If a cursor that is not a bit field declaration is passed in, or if the bit
+ * field's width expression cannot be evaluated, -1 is returned.
  */
 CINDEX_LINKAGE int clang_getFieldDeclBitWidth(CXCursor C);
 
diff --git a/clang/tools/libclang/CXType.cpp b/clang/tools/libclang/CXType.cpp
--- a/clang/tools/libclang/CXType.cpp
+++ b/clang/tools/libclang/CXType.cpp
@@ -10,11 +10,11 @@
 //
 //===--------------------------------------------------------------------===//
 
+#include "CXType.h"
 #include "CIndexer.h"
 #include "CXCursor.h"
 #include "CXString.h"
 #include "CXTranslationUnit.h"
-#include "CXType.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclObjC.h"
 #include "clang/AST/DeclTemplate.h"
@@ -371,6 +371,21 @@
   return ULLONG_MAX;
 }
 
+unsigned clang_isFieldDeclBitWidthDependent(CXCursor C) {
+  using namespace cxcursor;
+
+  if (clang_isDeclaration(C.kind)) {
+    const Decl *D = getCursorDecl(C);
+
+    if (const FieldDecl *FD = dyn_cast_or_null<FieldDecl>(D)) {
+      if (FD->isBitField() && FD->getBitWidth()->isValueDependent())
+        return 1;
+    }
+  }
+
+  return 0;
+}
+
 int clang_getFieldDeclBitWidth(CXCursor C) {
   using namespace cxcursor;
 
@@ -378,7 +393,7 @@
     const Decl *D = getCursorDecl(C);
 
     if (const FieldDecl *FD = dyn_cast_or_null<FieldDecl>(D)) {
-      if (FD->isBitField())
+      if (FD->isBitField() && !FD->getBitWidth()->isValueDependent())
         return FD->getBitWidthValue(getCursorContext(C));
     }
   }