diff --git a/lib/mathlib.cpp b/lib/mathlib.cpp
index 330305ba7..a7b3ead17 100644
--- a/lib/mathlib.cpp
+++ b/lib/mathlib.cpp
@@ -346,7 +346,7 @@ MathLib::biguint MathLib::toULongNumber(const std::string & str)
         const biguint ret = std::stoull(str, &idx, 10);
         if (idx != str.size()) {
             const std::string s = str.substr(idx);
-            if (s.find_first_not_of("LlUu") != std::string::npos && s != "i64" && s != "ui64")
+            if (!isValidIntegerSuffix(s, true))
                 throw InternalError(nullptr, "Internal Error. MathLib::toULongNumber: input was not completely consumed: " + str);
         }
         return ret;
@@ -426,7 +426,7 @@ MathLib::bigint MathLib::toLongNumber(const std::string & str)
         const biguint ret = std::stoull(str, &idx, 10);
         if (idx != str.size()) {
             const std::string s = str.substr(idx);
-            if (s.find_first_not_of("LlUu") != std::string::npos && s != "i64" && s != "ui64")
+            if (!isValidIntegerSuffix(s, true))
                 throw InternalError(nullptr, "Internal Error. MathLib::toLongNumber: input was not completely consumed: " + str);
         }
         return ret;
@@ -498,8 +498,9 @@ double MathLib::toDoubleNumber(const std::string &str)
     if (isIntHex(str))
         return static_cast<double>(toLongNumber(str));
 #ifdef _LIBCPP_VERSION
-    if (isFloat(str)) // Workaround libc++ bug at http://llvm.org/bugs/show_bug.cgi?id=17782
-        // TODO : handle locale
+    if (isFloat(str)) // Workaround libc++ bug at https://github.com/llvm/llvm-project/issues/18156
+        // TODO: handle locale
+        // TODO: make sure all characters are being consumed
         return std::strtod(str.c_str(), nullptr);
 #endif
     if (isFloatHex(str))
@@ -512,7 +513,9 @@ double MathLib::toDoubleNumber(const std::string &str)
         throw InternalError(nullptr, "Internal Error. MathLib::toDoubleNumber: conversion failed: " + str);
     std::string s;
     if (istr >> s) {
-        if (s.find_first_not_of("FfLl") != std::string::npos)
+        if (isDecimalFloat(str))
+            return ret;
+        if (!isValidIntegerSuffix(s, true))
             throw InternalError(nullptr, "Internal Error. MathLib::toDoubleNumber: input was not completely consumed: " + str);
     }
     return ret;
diff --git a/test/testmathlib.cpp b/test/testmathlib.cpp
index c651707e0..f3baa3bec 100644
--- a/test/testmathlib.cpp
+++ b/test/testmathlib.cpp
@@ -595,26 +595,19 @@ private:
         ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1L"),       0.001);
         ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1ll"),      0.001);
         ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1LL"),      0.001);
-        // TODO: need to succeed
-        //ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1u"),       0.001);
-        //ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1U"),       0.001);
-        //ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1ul"),      0.001);
-        //ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1UL"),      0.001);
-        //ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1ULL"),     0.001);
-        //ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1ULL"),     0.001);
-
-        // TODO: need to fail
-        // invalid values
-        //ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1f"),       0.001);
-        //ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1F"),       0.001);
-        //ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1.ff"),     0.001);
-        //ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1.FF"),     0.001);
-        //ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1.ll"),     0.001);
-        //ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1.0LL"),    0.001);
-        //ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1.0ff"),    0.001);
-        //ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1.0FF"),    0.001);
-        //ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1.0ll"),    0.001);
-        //ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1.0LL"),    0.001);
+        ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1u"),       0.001);
+        ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1U"),       0.001);
+        ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1ul"),      0.001);
+        ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1UL"),      0.001);
+        ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1ULL"),     0.001);
+        // TODO: make these work with libc++
+#ifndef _LIBCPP_VERSION
+        ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1i64"),     0.001);
+        ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1I64"),     0.001);
+        ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1ui64"),    0.001);
+        ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1UI64"),    0.001);
+        ASSERT_EQUALS_DOUBLE(1.0,    MathLib::toDoubleNumber("1I64"),     0.001);
+#endif
 
         ASSERT_EQUALS_DOUBLE(0.0,    MathLib::toDoubleNumber("0E+0"),     0.000001);
         ASSERT_EQUALS_DOUBLE(0.0,    MathLib::toDoubleNumber("0E-0"),     0.000001);
@@ -662,6 +655,28 @@ private:
         ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1 invalid"), InternalError, "Internal Error. MathLib::toDoubleNumber: input was not completely consumed: 1 invalid");
         ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("-1e-08.0"), InternalError, "Internal Error. MathLib::toDoubleNumber: input was not completely consumed: -1e-08.0");
 
+        // invalid suffices
+#ifdef _LIBCPP_VERSION
+        ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1f"), InternalError, "Internal Error. MathLib::toDoubleNumber: conversion failed: 1f");
+        ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1F"), InternalError, "Internal Error. MathLib::toDoubleNumber: conversion failed: 1F");
+        ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1.ff"), InternalError, "Internal Error. MathLib::toDoubleNumber: conversion failed: 1.ff");
+        ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1.FF"), InternalError, "Internal Error. MathLib::toDoubleNumber: conversion failed: 1.FF");
+        ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1.0ff"), InternalError, "Internal Error. MathLib::toDoubleNumber: conversion failed: 1.0ff");
+        ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1.0FF"), InternalError, "Internal Error. MathLib::toDoubleNumber: conversion failed: 1.0FF");
+#else
+        ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1f"), InternalError, "Internal Error. MathLib::toDoubleNumber: input was not completely consumed: 1f");
+        ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1F"), InternalError, "Internal Error. MathLib::toDoubleNumber: input was not completely consumed: 1F");
+        ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1.ff"), InternalError, "Internal Error. MathLib::toDoubleNumber: input was not completely consumed: 1.ff");
+        ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1.FF"), InternalError, "Internal Error. MathLib::toDoubleNumber: input was not completely consumed: 1.FF");
+        ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1.0ff"), InternalError, "Internal Error. MathLib::toDoubleNumber: input was not completely consumed: 1.0ff");
+        ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1.0FF"), InternalError, "Internal Error. MathLib::toDoubleNumber: input was not completely consumed: 1.0FF");
+#endif
+        // TODO: needs to fail
+        //ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1.ll"), InternalError, "Internal Error. MathLib::toDoubleNumber: input was not completely consumed: 1.ll");
+        //ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1.0LL"), InternalError, "Internal Error. MathLib::toDoubleNumber: input was not completely consumed: 1.0LL");
+        //ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1.0ll"), InternalError, "Internal Error. MathLib::toDoubleNumber: input was not completely consumed: 1.0ll");
+        //ASSERT_THROW_EQUALS(MathLib::toDoubleNumber("1.0LL"), InternalError, "Internal Error. MathLib::toDoubleNumber: input was not completely consumed: 1.0LL");
+
         // verify: string --> double --> string conversion
         ASSERT_EQUALS("1.0",  MathLib::toString(MathLib::toDoubleNumber("1.0f")));
         ASSERT_EQUALS("1.0",  MathLib::toString(MathLib::toDoubleNumber("1.0")));
@@ -986,6 +1001,7 @@ private:
         ASSERT_EQUALS(false, MathLib::isValidIntegerSuffix(""));
         ASSERT_EQUALS(false, MathLib::isValidIntegerSuffix("ux"));
         ASSERT_EQUALS(false, MathLib::isValidIntegerSuffix("ulx"));
+        ASSERT_EQUALS(false, MathLib::isValidIntegerSuffix("uu"));
         ASSERT_EQUALS(false, MathLib::isValidIntegerSuffix("lx"));
         ASSERT_EQUALS(false, MathLib::isValidIntegerSuffix("lux"));
         ASSERT_EQUALS(false, MathLib::isValidIntegerSuffix("lll"));