diff --git a/src/OpenFOAM/db/IOstreams/Sstreams/ISstream.C b/src/OpenFOAM/db/IOstreams/Sstreams/ISstream.C
index c2390f4ffa51448f7c19ddebc02c9740a646f279..0f87e251f53f255d81595c40dfbeac2df03d8326 100644
--- a/src/OpenFOAM/db/IOstreams/Sstreams/ISstream.C
+++ b/src/OpenFOAM/db/IOstreams/Sstreams/ISstream.C
@@ -149,7 +149,7 @@ void Foam::ISstream::readWordToken(token& t)
 
 Foam::Istream& Foam::ISstream::read(token& t)
 {
-    static const unsigned maxLen = 128;  // When parsing labels or scalars
+    constexpr const unsigned maxLen = 128; // Max length for labels/scalars
     static char buf[maxLen];
 
     // Return the put back token if it exists
@@ -404,7 +404,7 @@ Foam::Istream& Foam::ISstream::read(char& c)
 
 Foam::Istream& Foam::ISstream::read(word& str)
 {
-    static const unsigned maxLen = 1024;
+    constexpr const unsigned maxLen = 1024;
     static char buf[maxLen];
 
     unsigned nChar = 0;
@@ -483,7 +483,7 @@ Foam::Istream& Foam::ISstream::read(word& str)
 
 Foam::Istream& Foam::ISstream::read(string& str)
 {
-    static const unsigned maxLen = 1024;
+    constexpr const unsigned maxLen = 1024;
     static char buf[maxLen];
 
     char c;
@@ -583,7 +583,7 @@ Foam::Istream& Foam::ISstream::read(string& str)
 
 Foam::Istream& Foam::ISstream::readVariable(std::string& str)
 {
-    static const unsigned maxLen = 1024;
+    constexpr const unsigned maxLen = 1024;
     static char buf[maxLen];
 
     unsigned nChar = 0;
@@ -707,7 +707,7 @@ Foam::Istream& Foam::ISstream::readVariable(std::string& str)
 
 Foam::Istream& Foam::ISstream::readVerbatim(std::string& str)
 {
-    static const unsigned maxLen = 8000;
+    constexpr const unsigned maxLen = 8000;
     static char buf[maxLen];
 
     unsigned nChar = 0;
diff --git a/src/fileFormats/stl/STLCore.C b/src/fileFormats/stl/STLCore.C
index 9345bd246f6e9b67c53fd83a67b1a6c7930c0b1a..d0660d57575341118718c33148eb425e53294807 100644
--- a/src/fileFormats/stl/STLCore.C
+++ b/src/fileFormats/stl/STLCore.C
@@ -35,7 +35,7 @@ License
 //! \cond fileScope
 
 // The number of bytes in the STL binary header
-static const unsigned STLHeaderSize = 80;
+static constexpr const unsigned STLHeaderSize = 80;
 
 // Check if "SOLID" or "solid" appears as the first non-space content.
 // Assume that any leading space is less than 75 chars or so, otherwise