diff --git a/parse.c b/parse.c
index 91e73bc..f4f57aa 100644
--- a/parse.c
+++ b/parse.c
@@ -397,12 +397,22 @@ int parse_float(
 
     /* ufrac is now >= 2**55 and < 2**56 */
 
-    /* Round from FLT4 to FLT2 or single-word float */
+    /* Round from FLT4 to FLT2 or single-word float.
+     *
+     * +--+--------+-------+
+     * |15|14     7|6     0|
+     * +--+--------+-------+
+     * | S|EEEEEEEE|MMMMMMM|
+     * +--+--------+-------+
+     *  Sign (1 bit)
+     *     Exponent (8 bits)
+     *              Mantissa (7 bits)
+     */
     if (size < 4) {
         /* Round to nearest 8- or 24- bit approximation */
         ufrac += (1UL << (56 - (8 + 16*(size-1)) - 1));
 
-        if ((ufrac >> 56) > 0) {  /* Overflow? */
+        if ((ufrac >> 56) > 0) {       /* Overflow? */
             ufrac >>= 1;               /* Normalize */
             uexp--;
         }
diff --git a/tests/RunTests b/tests/RunTests
index e2edfa2..d14a063 100755
--- a/tests/RunTests
+++ b/tests/RunTests
@@ -14,6 +14,7 @@ TESTS="test-asciz \
     test-enabl-ama \
     test-enabl-lcm \
     test-endm \
+    test-float \
     test-if \
     test-impword \
     test-include \
diff --git a/tests/test-float.mac b/tests/test-float.mac
new file mode 100644
index 0000000..3459c0c
--- /dev/null
+++ b/tests/test-float.mac
@@ -0,0 +1,28 @@
+;;;;;
+;
+; Test floating point numbers
+
+        .word   ^F 1.0          ; 040200
+        .word   ^F-1.0          ; 140200
+        .word   -^F 1.0         ; 137600
+        .word   -^F-1.0         ; 037600
+
+        .word   ^F6.2           ; 040706
+        .word   ^C^F6.2         ; 137071
+        .word   ^C<^F6.2>       ; 137071
+
+        .flt2   6.2             ; 040706 063146
+        .flt4   6.2             ; 040706 063146 063146 063146
+
+        .flt2   1.5             ; 040300 000000
+        .flt4   1.5             ; 040300 000000 000000 000000
+
+        .word   ^F 72057594037927935  ; 056200 (rounded!)
+        .flt2   72057594037927935     ; 056200 000000 (rounded!)
+        .flt4   72057594037927935     ; 056177 177777 177777 177777 (exact!)
+
+        .word   ^F 72057594037927936  ; 056200
+        .flt2   72057594037927936     ; 056200 000000
+        .flt4   72057594037927936     ; 056200 000000 000000 000000
+
+        .flt4   72057594037927937     ; 056200 000000 000000 000001