diff --git a/src/common/fontcmn.cpp b/src/common/fontcmn.cpp
index 7767791433..cadf89b1e5 100644
--- a/src/common/fontcmn.cpp
+++ b/src/common/fontcmn.cpp
@@ -44,6 +44,8 @@
 
 #include "wx/tokenzr.h"
 
+#include <float.h>       // for FLT_MAX
+
 // debugger helper: this function can be called from a debugger to show what
 // the date really is
 extern const char *wxDumpFont(const wxFont *font)
@@ -758,9 +760,9 @@ bool wxNativeFontInfo::FromString(const wxString& s)
     token = tokenizer.GetNextToken();
     if ( !token.ToCDouble(&d) )
         return false;
-    pointSize = static_cast<float>(d);
-    if ( static_cast<double>(pointSize) != d )
+    if ( d < 0 || d > FLT_MAX )
         return false;
+    pointSize = static_cast<float>(d);
 
     token = tokenizer.GetNextToken();
     if ( !token.ToLong(&l) )
diff --git a/src/msw/font.cpp b/src/msw/font.cpp
index c54e2601ad..293c8e0324 100644
--- a/src/msw/font.cpp
+++ b/src/msw/font.cpp
@@ -43,6 +43,8 @@
 #include "wx/scopeguard.h"
 #include "wx/tokenzr.h"
 
+#include <float.h>       // for FLT_MAX
+
 // ----------------------------------------------------------------------------
 // constants
 // ----------------------------------------------------------------------------
@@ -692,10 +694,11 @@ bool wxNativeFontInfo::FromString(const wxString& s)
                 // lfHeight, as with v0 strings.
                 if ( !wxIsNullDouble(d) )
                 {
-                    pointSize = static_cast<float>(d);
-                    if ( static_cast<double>(pointSize) != d )
+                    if ( d < 0 || d > FLT_MAX )
                         return false;
 
+                    pointSize = static_cast<float>(d);
+
                     setPointSizeFromHeight = false;
                 }
             }
diff --git a/src/osx/carbon/font.cpp b/src/osx/carbon/font.cpp
index c1dcc0fda0..8504b4c609 100644
--- a/src/osx/carbon/font.cpp
+++ b/src/osx/carbon/font.cpp
@@ -31,6 +31,8 @@
 #include <map>
 #include <string>
 
+#include <float.h>       // for FLT_MAX
+
 #define TRACE_CTFONT "ctfont"
 
 class WXDLLEXPORT wxFontRefData : public wxGDIRefData
@@ -957,13 +959,13 @@ bool wxNativeFontInfo::FromString(const wxString& s)
     token = tokenizer.GetNextToken();
     if ( !token.ToCDouble(&d) )
         return false;
+    if ( d < 0 || d > FLT_MAX )
+        return false;
 #ifdef __LP64__
     // CGFloat is just double in this case.
     m_ctSize = d;
 #else // !__LP64__
     m_ctSize = static_cast<CGFloat>(d);
-    if ( static_cast<double>(m_ctSize) != d )
-        return false;
 #endif // __LP64__/!__LP64__
 
     token = tokenizer.GetNextToken();
diff --git a/tests/font/fonttest.cpp b/tests/font/fonttest.cpp
index b6cd5b60aa..f3e53ad74d 100644
--- a/tests/font/fonttest.cpp
+++ b/tests/font/fonttest.cpp
@@ -449,4 +449,28 @@ TEST_CASE("wxFont::NativeFontInfoUserDesc", "[font][fontinfo]")
         CHECK( test.GetEncoding() == temp2.GetEncoding() );
 #endif
     }
+
+    // Test for a bug with handling fractional font sizes in description
+    // strings (see #18590).
+    wxFont font(*wxNORMAL_FONT);
+
+    static const float sizes[] = { 12.0f, 10.5f, 13.8f, 10.123f, 11.1f };
+    for ( unsigned n = 0; n < WXSIZEOF(sizes); n++ )
+    {
+        font.SetFractionalPointSize(sizes[n]);
+
+        // Just setting the font can slightly change it because of rounding
+        // errors, so don't expect the actual size to be exactly equal to what
+        // we used -- but close enough.
+        const float sizeUsed = font.GetFractionalPointSize();
+        CHECK( sizeUsed == Approx(sizes[n]).epsilon(0.001) );
+
+        const wxString& desc = font.GetNativeFontInfoDesc();
+        INFO("Font description: " << desc);
+        CHECK( font.SetNativeFontInfo(desc) );
+
+        // Notice that here we use the exact comparison, there is no reason for
+        // a differently rounded size to be used.
+        CHECK( font.GetFractionalPointSize() == sizeUsed );
+    }
 }